JPH04199576A - Optical wiring integrated device - Google Patents

Abstract

PURPOSE:To enable speedup of channel signals by forming the optical path between a photoemitter and a photodetector of an optical waveguide provided with concave mirrors. CONSTITUTION:An optical path is formed by concave reflectors 14 between a photoemitter 11 and a photodetector 12 via a slab type waveguide 13. Preferably at this time the optical path should be parallel or at a right angle with an emitted beam from the photoemitter or with the stripe direction of a semiconductor laser as the photoemitter 11. Hereupon, light intersection in the slab type waveguide 13 undergoes no exchange of light modes nor light scattering, shows therefore no interference, and is indifferent to signal speed and the like. This causes no trouble on signal speedup.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to integrated optical wiring and provides a high-speed, high-density wiring system that is difficult to achieve with electrical wiring.

(Crystal art) With the development of an advanced information society, the amount of information handled increases year by year.
Accordingly, the speed (c bit rate) of communication transmission systems is also becoming faster. While public communication networks are currently constructed based on telephone lines, the development of a broadband digital subscriber network using image information as the main medium is being considered.

Among these, the electronic exchanger is positioned as a core device in the information transmission system, and efforts are being made to make it faster and wider by making full use of current large-scale integrated circuit technology. Figure 11 shows the board (11
3) Above is a conceptual diagram of the 64x64 electronic exchange switch under development. The passing signal rate is 155 Mbits per second. Due to the high speed of 155 Mbits per second, it is impossible with current integration technology to integrate all the elements on one chip due to heat generation capacity. Prepare 24 pieces and wire them electrically (rill) l, equivalently 6
A 4×64 electronic switching switch is being considered. However, at low speeds, even simple electrical wiring runs at 155 M/s.
As bit speeds increase, various problems arise. First, since the wiring intersection (114) is electrical, some kind of three-dimensional crossing is required. For example, the method of signal crossing using through-holes as shown in Figure 12 is simple and widely used, but for high-speed signals, electromagnetic radiation is large in the through-hole area, which can cause mutual interference. It becomes a factor that occurs.

In addition, in order to avoid using the through-hole method, it is possible to prepare multilayer wiring, for example, but this example requires an 8-layer board and has many problems including reliability. In order to ensure normal operation of the logic inside the switches, it is desirable that the wiring lengths connecting ×8 switches be uniform in length for accuracy of less than 1/10 of the clock rate. It is possible to make the other wires longer, but this has the disadvantage that the longer the wire length, the more mutual interference will occur. Additionally, the International Communications Standards Committee has revealed that the current signal speed is assumed to be 155 Mbits per second, but the next generation will have a signal speed of 600 Mbits or Z4Gbits.
Since mutual interference increases in proportion to the signal speed, it will become an increasing problem in the future. Another problem is that the increasing capacitance of electrical wiring makes it difficult for high-speed signals to propagate.

Optical signals are generally considered to have high speed, low IO, and little mutual interference. Optical wiring based on the same idea can be considered in this field as well. FIG. 13 is an example in which a ridge-type waveguide, which is the most common type for fiK light, is used instead of electrical wiring, and IE13 (3) shows the intersection. Because light has the property of traveling straight, it may seem that the signals cross without mutual interference, but the boundary conditions of the light change at the intersection of the waveguides, as shown in Figure 13 (
b) A conversion of the mode of light occurs as shown in K. As a result, there is a drawback that leakage occurs into the waveguides that partially intersect, resulting in mutual interference. This becomes a serious problem in a configuration in which a large number of optical waveguides intersect, such as in a 64×64 electronic exchange switch.

(Problem to be solved by the invention) In this way, problems such as mutual interference can be solved with conventional electrical wiring or optical wiring using ridge-type optical waveguides, but future high-speed electronic switching switches will require a new method. Wiring connection was desired.

[Structure of the invention]

(Means for Solving the Problems) An optical path is formed by at least a reflecting mirror having a concave surface structure via a slab waveguide between a light emitting element and a light receiving element. At this time, the optical path is parallel or perpendicular to the beam emitted from the light emitting element or the striping direction of the semiconductor laser serving as the light emitting element. The all-concave mirrors have the same shape, although their directions differ by 9011 points, and the total path length between the light-emitting element and the light-receiving element is the same. The concave mirror is formed by digging into the slab waveguide using a method such as dry etching. The difference in refractive index between the dug portion and the waveguide portion enables total reflection of light. Further, a metal film or the like is also attached if necessary. These forms integrate a light emitting element, a light receiving element, and an optical waveguide in a monolithic or hybrid manner. The wiring length is made uniform by making the physical length of the optical waveguide uniform or by adjusting the bias current value of the semiconductor laser and adjusting the light emission delay time of the optical output.

(Function) Crossing of light within the slab waveguide does not undergo mode conversion or scattering of light, so no mutual interference occurs.

And since it is unrelated to the speed of the signal, there is no problem with increasing the speed of the signal, as was the case with electrical signals.

Semiconductor lasers and PIN-type light receiving elements can operate relatively easily up to the IOG bit region, so they can sufficiently cope with future speed increases of electronic exchange switches. If a semiconductor laser with a low threshold value of several mA is used, it can be superior to electric wiring in terms of power consumption. It is easy to make the wiring length uniform, and extending the wiring does not increase interference. Further, fine adjustments such as cases where correction cannot be made using the physical length or correction of delays in the electronic circuit section can be easily performed by adjusting the bias current value of the semiconductor laser. By making the wiring optical path length uniform, it is possible to make the radius of curvature of the concave mirrors the same, that is, the basic concave mirrors can all have the same shape, and the design and manufacturing can be greatly simplified. Further, by making the optical path parallel or perpendicular to the stripe direction of the semiconductor laser, the concave mirrors need only be arranged in different directions by 90 degrees, thereby further simplifying the design and manufacturing. This is particularly effective in minimizing crystal orientation problems when producing a concave mirror by dry etching or the like.

(Example) The present invention will be described in detail below using the drawings.

FIG. 1 shows a basic conceptual diagram of the present invention, showing a case where the input and outputs of four 2×2 switches are interconnected to form a 4×4 switch configuration. An optical path (18) directly coupled only with a slab waveguide αJ, or bent with a concave mirror α◆, connects the light-emitting element array (11), where the light-emitting elements are indicated by ◎ marks, and the light-receiving element array α, whose light-receiving elements are indicated by O marks. This is an example in which an optical path αe is formed.

Figure 2 shows a semiconductor laser (2-a) and a photodiode (
2-c) and the layer structure of the slab waveguide (2-b). An example of monolithic integration using InP-based compound semiconductors is shown. Growth was performed three times by metal organic vapor phase epitaxy. The process is shown below. On an n-type InP substrate circle, there are three InGaAIP layers with different compositions, that is, a first guide layer of λq = 1.3 um in terms of emission wavelength, and an active layer of λq = L of 55 um (up to). , and λq=L3
Grow a second guide layer of um.

A diffraction grating (T) is formed on the second guide layer, and then a p-temperature InP cladding layer is regrown. The optical waveguide section is etched down to the substrate by wet etching, and then λQ=L3um
Further grow a waveguide layer @ and a high resistance InP layer. The photodiode section is essentially the same as the semiconductor laser section except that it does not form a diffraction grating. The laser part and the optical waveguide part were separated by dry etching (7), but they are not separated unless it is necessary to process a lens on the waveguide, which will be described later, while confining the current flowing to the laser.

The optical waveguide section forms a slab waveguide that propagates while repeating total reflection at the interface because the refractive index of the waveguide layer is 3 to 11 degrees higher than that of the InP cladding layers above and below it. It is clear that light crosses within the slab waveguide and does not have any effect. In terms of loss, if the wavelength of light emitted from the active layer is 11-55u, a waveguide with a loss of less than αsdB/m can be formed, so a waveguide with a maximum length of about 10 scratches can be formed. Furthermore, in the case of a short distance, the optical waveguide layer may have the same structure as the semiconductor laser layer.

FIG. 3 shows a concave mirror formed by dry etching. The reflecting surface of the concave mirror was the interface between the semiconductor and air. In
If the refraction of a P-based compound semiconductor is 15, the angle of total reflection of light incident from the semiconductor layer is 17f measured from the normal line at the reflection point.
It becomes ili degree. When the concave mirrors are arranged at 45 degrees to the optical path as shown in FIG. 1, all the concave mirrors satisfy the condition of total reflection, and as a result, a good optical path without leakage can be formed. Note that dry etching was performed as follows.

Insert the sample into a vacuum chamber, evacuate to below 10 Torr, ionize argon gas with a microwave output of 200 W, and irradiate the sample with an acceleration voltage of 400 μ for 1 minute to remove 20-40 angstroms of oxidation that adhered to the surface. Remove the film to expose a clean surface. After that, chlorine gas and argon gas were each flowed into the plasma chamber at a rate of 20 sec/min.
Electron cyclotron resonance is caused in the mixed gas under the conditions of microwaves of 200 W and a magnetic field of 875 Gauss, and an acceleration voltage of 40
Ion current density, 0,2
Irradiate the drawn sample at 4 mA/-. The total pressure is 1.6 x 10'' Torr. Under these conditions, the etching rate is 0.17 microns/min, so
A 30 minute etch was performed to form a 5 micron deep concave mirror.

FIG. 4 shows an embodiment in which the optical path length is made uniform. As mentioned above, it is necessary to make the optical path length uniform in order to normalize the operation of the logic in the 2×2 electronic switch at the subsequent stage. In addition, if the loss of the waveguide is finite, the received light power can be kept constant, and there is no need to adjust the gain below that of the photodiode or the output of the semiconductor laser. This is also a great advantage in terms of manufacturing the device. That is, as shown in the figure, if the optical path is made uniform and the optical path is bent only at right angles by concave mirrors, the concave mirrors can be formed in the same shape even though their directions are changed by 90 degrees. This simplifies the design and manufacture of elements including concave mirrors. Particularly when attempting to form a concave mirror by dry etching, it is extremely difficult to obtain a mirror surface in order to produce a vertical surface regardless of the orientation of the crystal and to reduce scattering. It is clear that the focal length of the concave mirror can be determined by calculating the optical path length so that the beam emitted from the light emitting element is focused on the surface of the light receiving element.

Taking the above into consideration, FIG. 5 shows a 4×4 optical wiring for an electronic exchange switch in terms of layers.

The figure shows an example in which the light-emitting element, light-receiving element, and optical waveguide are fabricated monolithically using a compound semiconductor, but it is also possible to form the light-emitting element, light-receiving element using a compound semiconductor, and the optical waveguide using silicon, and to integrate them in a hybrid manner. It's obvious.

If the emission wavelength is set to 1 um or less, the light receiving element can also be formed of silicon.

The beam emitted from the semiconductor laser is usually several 1 in the vertical and horizontal directions.
It is radiated with a 0 degree spread. The slab waveguide has a suppressing effect on vertical expansion, but it also suppresses horizontal expansion.
t-don't have it. If the distance from the light emitting element to the first concave mirror is long, it may cause mutual interference, so some kind of suppressing means is required. FIG. 6 shows an embodiment in which a lens processing (61) is applied to the light entrance of the optical waveguide. The lens was processed by dry etching. This step can be performed simultaneously when forming the concave mirror, and does not add to the number of steps. It is also possible to perform lens processing on a semiconductor laser to achieve the same effect. However, the processed surface is not very desirable because it also changes the resonance conditions of the laser as it is the resonator surface of the laser.

When considering an 8×8 electronic exchange switch configuration, the size of the optical wiring area may be about 1 (15) 1 based on the current integrated circuit scale. At this time, the current substrate size of compound semiconductors is about 3 inches at most. At this time, considering that the current substrate size of compound semiconductors is about 3 inches at most, it is not necessarily a good idea to use the same substrate. It is conceivable to use a split board. FIG. 7 shows an example of a configuration using a divided board. When the substrate is divided, the first possible method for coupling the waveguides is to directly couple them as they are. However, highly accurate alignment technology on the order of submicrons is required. The method shown in FIG. 7 is an example in which light-to-electricity or electricity-to-light conversion elements (71, 72) are arranged at the coupling point and electrically coupled therebetween. In this case, high precision alignment is not required and it can be said to be suitable for hybrid integration. The necessary semiconductor lasers and photodiodes may have similar structures. However, for the semiconductor laser, measures such as forming a highly reflective sI at the rear end are taken to prevent the beam emitted backward from being coupled to an adjacent photodiode. If the electrical output of the light-receiving element is small at this time, it may be possible to insert an amplifier (81) between the light-emitting element and the light-receiving element as shown in FIG.

FIG. 9 shows an example in which a waveguide type optical amplifier (91) is inserted on the optical path. The optical amplifier can be composed of a laser amplifier, but may also be an erbium-doped waveguide amplifier. Of course, in that case, a separate semiconductor laser for excitation is required. The optical amplifier may be placed anywhere in the optical path, but the noise characteristics will be better if it is placed as far back as possible in consideration of the saturation characteristics of the laser amplifier.

The means and effects of making the optical path length uniform were described above. Making the physical length uniform has great merits, but conversely it requires fine adjustment of the propagation delay time due to demands from electronic circuits41. In that case, it is possible to deal with this by adjusting the bias current value of the semiconductor laser. Figure 10 shows the pulse peak current value I for a semiconductor laser with a threshold of 4 mA.
The measurement results of the pulse response delay time with the bias current as a variable when the bias current is set to 2 mA are shown. 5 by adjusting the bias
This means that about 00 ps can be adjusted. This is the refractive index &
Considering the speed of light in the InP-based compound semiconductor of 5, it is approximately 4e.
K corresponds to the physical length of x*.

[Effects of the Invention] In the optical wiring using the slab waveguide according to the present invention, it is possible to cross optical signals without mutual interference, so it is possible to handle high-speed signals of 155 Mbits per second or more as communication channel signals, and to handle large signals of about 64 x 64. Scale integrated electronic switching switch circuits can also be formed. Its structure is simple, consisting of a semiconductor laser, a light receiving element, a slab waveguide, and a concave mirror formed in the waveguide. Due to the characteristics of semiconductor lasers, the present invention can operate satisfactorily even at speeds exceeding G bits per second, and there is no need to particularly change its constituent elements or arrangement to suit the speed. If a semiconductor laser or the like with a threshold value of several mA is used, the power consumption will be sufficiently lower than that of electrical wiring. Additionally, the optical path and concave mirror can be fabricated simultaneously using dry etching, making it suitable for mass production. Considering the above, the present invention can serve as a basic element for future high-speed large-scale electronic exchanges.

[Brief explanation of the drawing]

Figure 1 is a basic conceptual diagram, Figure 2 is the layered structure of the component semiconductor laser, photodiode, and slab waveguide.
Figure 3 is a diagram showing a concave mirror formed in a slab waveguide by dry etching, Figure 4 is a conceptual diagram with a uniform optical path, and Figure 5 is a diagram showing a concave mirror formed by dry etching in a slab waveguide.
The figure is a sketch showing the main parts of the present invention, Figure 6 is a diagram of the waveguide with lens processing, Figures 7 and 8 are conceptual diagrams of the substrate divided into parts, and Figure 9 is Figure 10 shows the bias dependence of the delay time in the pulse response of a semiconductor laser.
1, 12, and 13 are diagrams showing conventional examples and their problems. 11.--light emitting element array, 12... light receiving element array,
13... Slab waveguide, 14... Concave mirror, 15...
- Straight waveguide, 16... Right angle waveguide, 61... Lens processed into a waveguide, 71... Light to electricity conversion element, 72... Electricity to light conversion element, 81 ...
Electrical amplifier, 91... Optical amplifier. Agent Patent Attorney Noriyuki Chika / 4 Figure 1 Figure 4 2-Yu 2-b 2
-CFigure 2Figure 3Figure 5Figure 6Figure 7Figure 8Figure 9Figure f23 4 s /Verz/Tl1n<mA>Figure 10Figure 11Figure 12

Claims (1)

[Scope of Claims] (1) An optical wiring integrated device characterized in that an optical path between a light emitting element and a light receiving element is formed by an optical waveguide provided with a concave mirror. (2) The optical wiring integrated device according to claim 1, wherein the optical path is parallel or perpendicular to the direction of light emission from the light emitting element or the stripe direction of the semiconductor laser as the light emitting element. (3) The optical wiring integrated device according to claim 1, wherein the lengths of the plurality of optical paths coupling between the corresponding light emitting element and the light receiving element are the same. (4) The optical wiring integrated device according to claim 1, wherein the concave mirror has a focal length shorter than a maximum optical path length between the light emitting element and the light receiving element. (5) The optical wiring integrated device according to claim 1, wherein the radius of curvature of the concave mirror is designed so that the light emitted from the light emitting element is focused on a light receiving area of the light receiving element. (6) the concave mirror is formed by digging into the optical waveguide;
2. The optical wiring concentrating device according to claim 1, wherein light is reflected due to a difference in refractive index between the optical waveguide portion and the dug portion. (7) The optical wiring integrated device according to claim 6, characterized in that a metal film or a dielectric layer is attached to the portion dug into the optical waveguide to increase the reflectance of the concave mirror. (8) The optical wiring integrated device according to claim 1, wherein the optical waveguide is a slab waveguide. (9) The optical wiring integrated device according to claim 8, wherein the layer structure of the slab waveguide is the same as the basic layer structure of the light emitting device. (10) The optical wiring integrated device according to claim 1, wherein the light emitting device, the light receiving device, and the waveguide are integrated. (11) The optical wiring integrated device according to claim 10, wherein the light emitting device, the light receiving device, and the optical waveguide are monolithically integrated. (12) The optical wiring integrated device according to claim 10, wherein only the light emitting element and the light receiving element are made of a compound semiconductor. (13) The optical wiring integrated device according to claim 10, wherein the light emitting element, the light receiving element, and the waveguide, which are formed on separate substrates, are hybridly integrated on the same substrate. (14) The optical wiring integrated device according to claim 1, wherein the light emitting part of the light emitting element or the light entering part of the optical waveguide is processed with a lens for converging light. (15) The optical wiring integrated device according to claim 1, wherein the substrate on which the light emitting device, the light receiving device, and the optical waveguide are integrated is divided into a plurality of pieces. (16) When the optical path is coupled between the divided substrates, a light-to-electricity conversion element and an electricity-to-light conversion element are arranged and electrically connected at the joint.
The optical wiring integrated device described above. (17) Claim 1 characterized in that the bias current value of the semiconductor laser as the light emitting element is adjusted to adjust the propagation delay time of a signal on the optical path from the semiconductor laser to the optical waveguide and the light receiving element. The optical wiring integrated device described above. (18) The optical wiring integrated device according to claim 1, wherein an optical amplification element is formed on the optical path.