JPH05241049A - Optical module - Google Patents

Abstract

PURPOSE:To provide an optical module which is small in size, whose cost is low and which is excellent in mass-productivity. CONSTITUTION:A hologram optical element 10 is arranged between an optical fiber terminal 14 and a supporting base 13 where a semiconductor laser 11 and a PIN photodiode 12 are mounted. As for the optical element 10, a diffraction grating 16 is formed on one surface of a substrate and a lens 17 is formed on the other surface of the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication module, and more particularly to an optical module in which light emitting and light receiving elements are integrated.

[0002]

2. Description of the Related Art With the development of ISDN (Integrated Digital Network) in the field of public communication networks, large-capacity transmission of digital telephone services and image information of dozens of lines not only to trunk lines but also to end subscribers. It is expected to be required. In such high-speed and large-capacity transmission, it is considered that it is essential to realize an optical subscriber system by introducing an optical transmission technique, because the transmission using the conventional metallic cable is not enough.

One of the methods for realizing this optical subscriber system is the same wavelength bidirectional transmission method. This is bidirectional transmission with a single optical fiber connecting a station and a subscriber terminal, and N-ISDN.
It provides a service.

FIG. 10 shows an example of a conventional transmitting / receiving optical module used in the same wavelength bidirectional transmission system. This transmitting / receiving optical module includes a transmitting semiconductor laser module 1, a receiving photodiode module 2, and respective pigtail fibers 3 and 4 with an optical connector 5.
And a fiber fusion-bonding type 3 dB splitter 7 connected via 6.

In such a structure, the transmission signal 8 converted into light by the semiconductor laser module 1 is sent to the transmission line through the splitter 7. On the contrary, the received signal 9 arrived from the transmission path is split into two by the splitter 7, and one of them is converted into an electric signal by the receiving photodiode module 2. However, it has been difficult to realize the downsizing, cost reduction, and mass production required by the optical subscriber system with the optical branching / combining / multiplexing / demultiplexing device in which such individual optical components are combined.

Generally, in the optical subscriber system, one end of the optical terminal device is arranged on each subscriber side. Therefore, the optical module is required to be miniaturized so as to have a size equivalent to that of the conventional metallic cable terminal device. On the station side as well, since the number of terminals in the subscriber system increases enormously as compared with the trunk system, downsizing of the optical module is also required. In addition, in order to replace with a terminal device for a metallic cable having the same function, it is important that it can be manufactured at a lower cost. Further, a large increase in production capacity is required to arrange an optical terminal device in each subscriber's house and telephone station, and an optical module suitable for mass production is required.

[0007]

However, in the conventional transmitting / receiving optical module, since the optical components having a single function are combined, each of the semiconductor laser module 1, the receiving photodiode module 2 and the splitter 7 can be used independently. It had to be environmentally friendly and strong, and the size was inevitably increasing. Further, it is necessary to make extra space for accommodating the pigtail fibers 3 and 4 connecting the optical components. Further, the semiconductor laser module 1 and the receiving photodiode module 2 each require optical axis adjustment / fixing with an accuracy of μm unit, respectively.
Moreover, since the splitters 7 must be fused and stretched one by one, the cost is high and mass production is difficult.

An object of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to provide an optical module which is small in size, low in cost, and excellent in mass productivity.

[0009]

An optical module according to a first aspect of the present invention includes a support base on which a semiconductor laser device and a photodiode device are mounted, an optical fiber terminal, and a space between the support base and the optical fiber terminal. And a hologram optical element in which a diffraction grating is formed on one surface of the substrate and a lens is formed on the other surface of the substrate, and the diffraction grating surface of the hologram optical element is emitted from the semiconductor laser element. The transmitted light is optically coupled to the optical fiber terminal through the lens described above, is emitted from the fiber terminal, and the light diffracted by the diffraction grating surface of the hologram optical element is optically transmitted to the photodiode element through the lens. It is configured to be combined with.

According to another aspect of the invention, there is provided an optical module in which a semiconductor laser element and a photodiode element are mounted on a support, an optical fiber terminal, and the support is disposed between the support and the optical fiber terminal. A hologram optical element in which a diffraction grating is formed on one surface and a lens is formed on the other surface of the substrate. Light emitted from a semiconductor laser element and diffracted by the diffraction grating surface of the hologram optical element is a lens. The light optically coupled via the optical fiber terminal, emitted from the fiber terminal, and transmitted through the diffraction grating surface of the hologram optical element is optically coupled via the lens.

According to a third aspect of the present invention, the diffraction grating of the holographic optical element has a sawtooth cross section.

[0012]

As described above, according to the present invention, the hologram optical element constitutes the splitter for splitting and converging the incoming and outgoing light rays into the transmitted light and the diffracted light. Since the diffraction grating of this hologram optical element functions with a thickness of several μm, the splitter can be significantly downsized. Also, by mounting the semiconductor laser device and the photodiode device on the same support, and arranging them so that the light beams transmitted and diffracted by the hologram optical device are coupled to each other, the optical connection distance between each device is greatly increased. Can be shortened to

Furthermore, since the hologram optical element can be manufactured in a large-diameter substrate in a lump and cut out according to the diameter of the light beam to be used, it is suitable for mass production and cost reduction is easy. Further, since the distance between the semiconductor laser element and the photodiode element and the diffraction angle of the hologram optical element are set to be constant in advance, the optical elements can be coupled by adjusting and fixing the optical axis only once.
Man-hours can be reduced significantly.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a vertical sectional view showing an embodiment of an optical module according to the present invention. The hologram optical element 10 is arranged between the optical fiber terminal 14 and the support 13 on which the semiconductor laser 11 and the PIN photodiode 12 are mounted. The tip of the input / output optical fiber terminal 14 is optically polished obliquely at an angle of 3 to 7 ° in order to reduce reflected return light. In addition, the hologram optical element 10, the semiconductor laser 11, the PIN photodiode 12, the support 13,
The optical fiber terminal 14 is held in a package 15.

As shown in detail in FIG. 2, the hologram optical element 10 has a diffraction grating 16 formed on one surface of a substrate and a lens 17 formed on the other surface of the substrate. The diffraction grating 16 of this hologram optical element 10 is
As shown in FIG. 3, a constant spacing Λ formed on the substrate surface.
When a coherent laser beam 18 having a wavelength λ is incident, it is separated into a transmitted light 19 that travels straight and a diffracted light 20. The direction of the diffracted light 20 satisfies the following relational expression.

[0016]

[Equation 1]

Focusing on the + ^1st order diffracted light 20, the diffraction angle is θ _H = sin ⁻¹ (λ / Λ). Therefore, the distance between the diffraction grating 16 and the semiconductor laser 11 is set to l _H
Then, by setting the distance d between the semiconductor laser 11 and the PIN photodiode 12 as follows, the transmitted light 19
The semiconductor laser 11 and the + 1st order diffracted light 20 can be coupled to the PIN photodiode 12.

[0018]

[Equation 2]

The hologram can be produced by a method other than the usual interference exposure method, such as a method of calculating the interference fringe pattern by a computer to produce a photomask and producing it on a substrate such as glass by a photolithography method. There is a method of forming a mold by a method and injecting a plastic material such as a resin to transfer the material, and mass production can be performed at a very low cost.

On the other hand, the lens 17 can be manufactured by the ion exchange method according to the procedure shown in FIGS. That is, first, as shown in FIG. 4, a metal mask 22 having an opening smaller than the lens diameter is provided on the substrate 21. By immersing the substrate 21 in an alkaline solution 23 such as potassium as shown in FIG. 5, the refractive index of the portion 24 of the substrate 21 in which potassium ions are ion-exchanged is increased, and as shown in FIG. A hemispherical distributed index type plano-convex lens 25 is formed. The focal length can be changed by controlling the amount of ion exchange.

Further, as shown in FIG. 7, wet etching is performed after the ion exchange to form the biconvex lens 26 on the substrate 21 by utilizing the property that the etching rate of the substrate becomes slow in inverse proportion to the exchanged ion concentration. You can also do it. Further, as shown in FIG. 8, the Fresnel lens 27 can be formed on the substrate 21 by a concentric Fresnel zone plate by dry etching or a transfer method using a die.

FIG. 9 shows an example of the mounting structure of the semiconductor laser 11 and the PIN photodiode 12. The semiconductor laser 11 is fixed to the upper surface of the support 13 for emitting light from the end face 28 of the chip, and the PIN photodiode 12 is fixed to the side surface of the support 13 because the light receiving surface 29 is on the chip surface. The semiconductor laser 11 and the PIN photodiode 12 are electrically insulated from each other in order to prevent crosstalk. The semiconductor laser 11 and the PIN photodiode 12 are connected to the bonding pads 30 and 31 via the bonding wires 32 and 33. The center distance between the semiconductor laser 11 and the PIN photodiode 12 is set to the distance d obtained by the equation (2).

In FIG. 1, of the transmission signal light modulated by the semiconductor laser 11 by the input electric signal, the light condensed by the lens 17 and transmitted without being diffracted by the diffraction grating 16 is transmitted from the optical fiber terminal 14 to the optical fiber 34. Is incident on
It is sent to the transmission line. Also, of the received signal light that has arrived from the transmission path, the light diffracted in the θ _H direction by the diffraction grating 16 is PI
The light enters the N photodiode 12 and is converted into an output electric signal. The transmitted component of the received signal light is the semiconductor laser 11
Is also incident on. However, the received signal light is greatly attenuated in the transmission line, is weaker than the LD output light, and the transmission speed of the optical subscriber system is 100 Mb / s at most. For this reason, the influence of the reception signal light incident on the modulation characteristics of the semiconductor laser 11 can be ignored.

The loss of the diffraction grating 16 that splits the transmitted and received light is determined by the ratio of the light that is transmitted without being diffracted in the case of transmission. In the case of reception, it is determined by the ratio of the + 1st order diffracted light 20 diffracted in the θ _H direction. In order to reduce the loss of the hologram diffraction grating type splitter, it is important to reduce unnecessary higher order diffracted light. For this purpose, the diffraction grating 16 of the hologram optical element 10 is formed into a sawtooth shape as shown in FIG. 3, and the diffraction angle θ _H is equal to the refraction angle obtained by Snell's law in a minute area of the sawtooth surface. The technique of blazing is effective. The saw-toothed angle, that is, the blaze angle θ _B is obtained by the equation (1) and the following equation representing Snell's law.

[0025]

[Equation 3]

From the above, by setting the blaze angle θ _B as the following equation, diffracted light other than the + 1st order can be suppressed.

[0027]

[Equation 4]

By this blazing method, it is possible to obtain a hologram diffraction grating type splitter having a very low loss of transmitted light passage loss of 4 dB and + 1st order diffracted light passage loss of 4 dB.

Since the diffraction angle of the diffraction grating 16 has wavelength dependency as shown in the equation (1), when the wavelength of the received signal changes, the + 1st order diffracted light 20 coupled to the PIN photodiode 12 also changes. However, since the light receiving surface 29 of the PIN photodiode 12 has a diameter of about 100 μm, the wavelength dependence of this diffracted light does not matter. Similarly, a mounting error of the center distance d between the semiconductor laser 11 and the PIN photodiode 12 can be absorbed by the PD light receiving diameter.

In the above configuration, the case where the diffraction grating 16 is arranged on the optical fiber terminal 14 side has been described.
The present invention is not limited to this, but the same effect can be obtained when the diffraction grating 16 is arranged on the support base 13 side.
The same effect can be obtained even in the case of a two-lens collimating optical system.

In the configuration according to the present invention, the splitter for performing bidirectional transmission and the coupling optical system are remarkably downsized, and the transmitting / receiving optical module can be realized in the same size as the conventional LD module alone. Further, the hologram optical element 10 can be mass-produced by a batch process using an inexpensive material by a photolithography method or a transfer method using a mold, and the cost can be significantly reduced as compared with the conventional one.

[0032]

As described above, according to the optical module of the present invention, the supporting base on which the semiconductor laser device and the photodiode device are mounted, the optical fiber terminal, and the supporting base and the optical fiber terminal are provided. And a hologram optical element in which a diffraction grating is formed on one surface of the substrate and a lens is formed on the other surface of the substrate, which is significantly smaller and less expensive than the conventional one.
Moreover, there is an effect that an optical module excellent in mass productivity can be provided.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an optical module according to the present invention.

FIG. 2 is a perspective view of the hologram optical element used in FIG.

FIG. 3 is a side view illustrating the operation of the diffraction grating of the hologram optical element.

FIG. 4 is a cross-sectional view showing an example of a procedure for manufacturing a lens.

FIG. 5 is a diagram showing an example of a procedure for manufacturing a lens.

FIG. 6 is a diagram showing an example of a procedure for manufacturing a lens.

FIG. 7 is a sectional view showing another embodiment of the lens.

FIG. 8 is a cross-sectional view showing still another embodiment of the lens.

FIG. 9 is a perspective view showing an example of a mounting structure of a semiconductor laser and a photodiode.

FIG. 10 is a schematic configuration diagram showing an example of a conventional transmitting / receiving optical module.

[Explanation of symbols]

 10 Holographic Optical Element 11 Semiconductor Laser 12 PIN Photodiode 13 Support 14 Optical Fiber Terminal 16 Diffraction Grating 17 Lens

Claims (3)

[Claims] 1. A support base on which a semiconductor laser device and a photodiode device are mounted, an optical fiber terminal, and a diffraction grating is formed between the support base and the optical fiber terminal and on one surface of a substrate. And a hologram optical element having a lens formed on the other surface of the substrate, and the light emitted from the semiconductor laser element and transmitted through the diffraction grating surface of the hologram optical element is optically transmitted to the optical fiber terminal through the lens. Coupled to and emitted from the fiber end,
An optical module, wherein light diffracted by a diffraction grating surface of a hologram optical element is optically coupled to a photodiode element via the lens. 2. A support base on which a semiconductor laser device and a photodiode device are mounted, an optical fiber terminal, and a diffraction grating is formed between the support base and the optical fiber terminal and on one surface of the substrate. And a hologram optical element having a lens formed on the other surface of the substrate, and the light emitted from the semiconductor laser element and diffracted by the diffraction grating surface of the hologram optical element is optically transmitted to the optical fiber terminal through the lens. The optical module is characterized in that light that is optically coupled, is emitted from a fiber terminal, and is transmitted through the diffraction grating surface of the hologram optical element is optically coupled to the photodiode element via the lens. 3. The optical module according to claim 1 or 2, wherein the diffraction grating of the hologram optical element is formed in a sawtooth cross-sectional shape.