JPH06138322A - Optical module - Google Patents

Abstract

PURPOSE:To provide the optical module for signal transmission and reception which is small in size, low in cost and excellent in mass productivity. CONSTITUTION:A hologram optical element (HOE) 11 is disposed between a supporting base 14 packaged with a semiconductor layer (LD) 12 and a pin photodiode (PD) 13 and an optical fiber terminal 17. This HOE includes a hologram diffraction grating 15 formed on a substrate, a lens 16 formed on the rear surface of the substrate and an interference film filter 17. Of the transmission signal light from the LD 12, the transmitted light which is condensed by the lens 16 and rectilinearly advances the hologram diffraction grating 15 is made incident on an optical fiber 18 and is further transmitted to a transmission path. Of the transmission signal light arriving at the HOE 11 from the transmission path, the light diffracted by the hologram diffraction grating 15 is made incident on the PD 13 and is converted to an output electric signal. The signal light 6 of another wavelength band from the optical fiber 19 is reflected and multiplexed by the interference film filter 17 and is sent from the optical fiber 18 to the transmission path.

Description

Detailed Description of the Invention

[0001]

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

[0002]

In the field of public communication networks, ISDN
It is expected that with the progress of the above, transmission of a large amount of information such as digital telephone service of several tens of lines and image information will be required not only to the trunk line system but also to the end subscriber system. In such high-speed, large-capacity information transmission, it is considered necessary to realize an optical subscriber system by introducing an optical transmission technique, because conventional transmission using a metallic cable is not enough.

One of the methods for realizing this optical subscriber system is the same wavelength bidirectional transmission method. This is a single optical fiber connecting a station and a subscriber terminal for bidirectional information transmission and N-
It provides ISDN service. Furthermore, this N
In addition to ISDN, it is also required to realize image information transmission in a broadcasting mode such as CATV by wavelength multiplexing.

FIG. 6 is a block diagram of a conventional transmitting / receiving optical module used in the same wavelength bidirectional transmission system to which the above-mentioned wavelength multiplexing function is added.

This optical module includes a semiconductor laser module 71 which generates a transmission signal light 4 of 1.3 μm band, a photodiode module 72 which receives the same reception signal light of 1.3 μm band, and pigtails of the modules 72 and 73. Fiber-fusion type 3 dB connected to the fiber
It comprises a splitter 73 and a fiber fusion type WDM coupler 74. The 1.3 μm-thick transmission signal light 4 converted into light by the semiconductor laser module 71 is sent to the transmission path through the 3 dB splitter 73 and the WDM coupler 74. On the contrary, the received signal light 5 in the 1.3 μm band, which has arrived from the transmission line, passes through the WDM coupler 74 and then becomes 3
The light is split into two by the dB splitter 73, and one of them is converted into an electric signal by the photodiode module 72. The wavelength-multiplexed signal light 6 in the 1.55 μm band is multiplexed / demultiplexed by the WDM coupler 74 and connected to the transmission line.

However, in such an optical module in which optical components such as individual optical branching / merging and multiplexing / demultiplexing elements are combined, it is not possible to realize the miniaturization, cost reduction and mass production required in the optical subscriber system. Have difficulty.

[0007]

In the optical subscriber system, one end of the optical terminal device including the above-mentioned optical module is placed on each subscriber side. Therefore, the optical module is required to be miniaturized so as to have the same size as the conventional metallic cable terminal device. Also on the station side, in the subscriber system, the number of terminals will increase enormously as compared with the trunk system, so that miniaturization of the optical module is also required.

Further, in order to replace the optical terminal device with a metallic cable terminal device having the same function,
It is important that it can be manufactured at a lower cost.

Further, in order to dispose the optical terminal device in each subscriber's house and telephone station, it is necessary to greatly increase the production capacity, and an optical module suitable for mass production is required.

However, the conventional transmitting / receiving optical module is
Since it is configured by combining optical components with a single function, semiconductor laser, photodiode, splitter, WD
Each of the M couplers needs to have environment resistance and strength, which inevitably increases the size. In addition, it is necessary to make extra space for accommodating the pigtail fiber connecting the optical components.

Further, the semiconductor laser and the photodiode are required to individually adjust and fix the optical axis with an accuracy of μm unit, and further, the splitter and the WDM coupler have to be fused and stretched one by one, thereby reducing the cost. -Not a structure suitable for mass production.

Therefore, an object of the present invention is to eliminate the drawbacks of the prior art transmitting / receiving optical module, and
An object of the present invention is to provide an optical module for transmission / reception that is low in cost and excellent in mass productivity.

[0013]

An optical module according to the present invention is provided with a first transmitted straight light and a first transmitted straight light which transmits the first light of a first wavelength received on the surface of a substrate from the straight direction in the straight direction. The first transmitted diffracted light which is diffracted and is reflected by the second light of the second wavelength received from the first direction on the surface of the substrate in the straight direction and received by the back surface of the substrate from the straight direction. A hologram optical element that transmits a third light of a wavelength in the straight traveling direction and transmits a fourth light of the first wavelength received from the first direction to the back surface of the substrate in the straight traveling direction; and the hologram optical element of the hologram optical element. On the back surface of the substrate, the third or fourth
And a semiconductor laser that supplies any of the light of (1) and a transmission that optically couples either of the third or fourth light generated in the straight traveling direction of the substrate surface of the hologram optical element to the first optical fiber. A signal light coupling means and a second signal light coupling means for coupling the second light from the second optical fiber to the hologram optical element are provided.

The optical module may further include a photodiode that receives either the first transmitted straight light or the transmitted diffracted light generated on the back surface of the substrate of the hologram optical element.

Further, one of the hologram optical elements is a diffraction grating formed on the back surface of the substrate for diffracting the light of the first wavelength and a diffraction grating formed on the front surface of the substrate for transmitting the light of the first wavelength. An interference film filter that reflects light of the second wavelength and a lens that is formed between the diffraction grating and the interference film filter to collect the light of the first wavelength are provided.

[0016]

In the optical module of the present invention, the hologram optical element constitutes an optical splitter for splitting and condensing the 1.3 .mu.m band incoming and outgoing light into the transmitted light and the diffracted light. The hologram diffraction grating with a built-in hologram optical element has a thickness of several μm.
Since it works with, the splitter can be significantly downsized. The light branched by the hologram diffraction grating is converged on different points by microlenses formed on one surface of the substrate of the optical element. An interference film filter formed on the other surface of the substrate reflects the signal light in the 1.55 μm band before entering the hologram diffraction grating, and
It can combine and split two lights.

Furthermore, the semiconductor laser and the receiving photodiode are mounted on the same support, and the optical beams transmitted and diffracted by the hologram optical element are arranged so as to be coupled to each other, whereby the optical connection distance between the elements is increased. It can be greatly shortened.

The hologram optical element can be manufactured in a batch on a large-diameter substrate and can be cut out according to the diameter of the light beam to be used. Therefore, the hologram optical element is suitable for mass production and cost reduction is easy.

Further, in the optical module of the present invention, the distance between the semiconductor laser and the receiving photodiode and the diffraction angle of the hologram element are set to be constant in advance, so that the coupling of these optical elements is adjusted only once. It can be fixed, and the man-hours for adjustment can be significantly reduced.

Therefore, according to the present invention, it is possible to obtain a transmission / reception optical module which is very small in size, low in cost, and excellent in mass productivity.

[0021]

The present invention will be described below with reference to the drawings.

FIG. 1 is a vertical sectional view of an embodiment of the present invention.

This optical module comprises a hologram optical element (HOE) 11, a semiconductor laser (LD) 12 and a P.
Support base 1 for supporting the IN photodiode (PD) 13
4 and the collimating and focusing collimating lenses 20 and 21. Further, the tips of the optical fiber terminal 22 for inputting / outputting the reception signal light and the transmission signal light in the 1.3 μm band and the optical fiber terminal 23 for the signal light 6 in the 1.55 μm band are 3 to 7 in order to reduce the reflected return light. Optically polished at an angle of °.

Before explaining the operation of the optical module shown in FIG. 1, the HOE 11 which is an important component and the LD 12 and PD 1 mounted on the semiconductor package 25 are described.
3 will be described in advance.

FIG. 2 is a perspective view of the HOE 11 used in the embodiment.

The HOE 11 includes a hologram diffraction grating 15 formed on the substrate 11a, a lens 16 formed on the back surface of the substrate 11a, and an interference film filter 17.

The interference film filter 17 is a multilayer film of TiO ₂ and SiO ₂ formed by vacuum deposition, and has a thickness of 30d.
Crosstalk of B or more transmits 1.3 μm light,
Reflects 5 μm light. The back surface of the substrate 11a on which the interference film filter 17 is formed is polished at an angle slightly inclined with respect to the surface of the substrate 11a on which the hologram diffraction grating 15 is formed.

FIG. 3 is an explanatory view of the operation of the hologram diffraction grating 15 formed on the HOE 11.

The hologram diffraction grating 15 is a diffraction grating having a periodic structure formed on the surface of the substrate 11a and having a constant interval Λ, and is a coherent laser beam (incident light) having a wavelength λ.
When 1 is incident, it is separated into a transmitted light 2 that travels straight and a diffracted light 3. The direction θ of the diffracted light 3 satisfies the expression (1).

Λ sin θ = nλ (n = 0, ± 1, ± 2, ± 3, ...) (1) Here, focusing on the + 1st order (n = + 1) diffracted light, the diffraction angle is θ _H = sin. ^-1 (λ / Λ). Therefore, FIG.
Let l _H be the distance between the hologram diffraction grating 15 and the LD 12 in, the distance d between the LD 12 and the PD 13 is (2)
By using the formula, the transmitted light 2 can be coupled to the LD 12 and the + 1st order diffracted light 3 can be coupled to the PD 13.

D = l _H × tan θ _H = {λ ² / (Λ ² −λ ² )} ^1/2 × l _H (2) The hologram diffraction grating 15 is used as an optical splitter. The cross-sectional shape of the grating is formed into a sawtooth shape so that the loss is extremely low, and unnecessary high-order diffracted light is reduced. That is, a blazing method is used in which the diffraction angle θ _H and the refraction angle obtained by Snell's law in the minute area of the sawtooth surface are matched. This saw-toothed angle, that is, the blaze angle θ _B is obtained by the equation (1) and the equation (3) representing Snell's law.

N ₁ sin θ ₁ = n ₂ sin θ ₂ (3) From the above, by setting the blaze angle θ _B by the equation (4), +
Diffracted light other than the first order can be suppressed.

Tan θ _B = λ / {nΛ− (Λ ² −λ ² ) ^1/2 } (4) (where n in the formulas (3) and (4) is the refractive index of the hologram substrate).

By this blazing method, the hologram optical element 11 shown in FIG. 2 can be used as a hologram diffraction grating splitter having a very low loss of transmitted light transmission loss of 4 dB and + 1st order diffracted light transmission loss of 4 dB.

The hologram diffraction grating 15 described above can be produced by a method other than the usual interference exposure method, such that a photomask is produced by calculating an interference fringe pattern by a computer, and a substrate 11a such as glass is formed by a photolithography technique.
And a method of forming a mold by the above-mentioned method and injecting a plastic material such as a resin for transfer, and it is possible to mass-produce at a very low cost.

FIG. 4 is a diagram showing one of the steps for producing the lens 16 shown in FIG. 2, that is, the procedure for producing the lens 16 by the ion exchange method.

First, a metal mask 42 having an opening smaller than the diameter of the lens 16 is provided on the substrate 11a (Fig. (A)). When this substrate 11a is dipped in an alkaline solution 43 such as potassium, the refractive index of a portion (ion exchange portion) 44 in which potassium ions are ion-exchanged in the substrate 11a is increased (Fig. (B)), resulting in a hemispherical distribution. A plano-convex lens 45 having a refractive index is formed. The focal length of the lens 45 can be changed by controlling the amount of ion exchange. The plano-convex lens 45 serves as the lens 16 in the hologram optical element 11.

FIG. 5 shows the LD 12 in the semiconductor package 25.
3 is a perspective view showing an example of a mounting structure of PD 13 and PD 13. FIG.

The LD 12 is fixed to the upper surface of the support 14 for emitting the transmission light 67 from the chip end surface 61 of the LD 12, and
D13 is fixed to the side surface of the support 14 because the light receiving surface 62 for receiving the received light 68 is on the chip surface of itself. In order to prevent crosstalk, the LD 12 and the PD 13 are electrically insulated. The center distance between the LD 12 and the PD 13 is set to the distance d calculated by the equation (2).

In FIG. 1, of the 1.3 μm band transmission signal light modulated by the LD 12 by the input electric signal, the light collimated by the lens 16, diffracted by the hologram diffraction grating 15 and transmitted straight through is collimated lens 20. Is collected by the optical fiber 18, enters the optical fiber 18 from the optical fiber terminal 22, and is further sent to the transmission path. On the contrary, 1.3μ that went backward from the transmission path and reached the HOE 11
Of the m-band received signal light, the hologram diffraction grating 15 is used to generate the signal shown in FIG.
The light diffracted in the θ _H direction at is incident on the PD 13,
The PD 13 converts the output electric signal.

The transmitted light 2 of the received signal light is L
It also enters D12. However, the received signal light is greatly attenuated in the transmission line and is weaker than the output light of the LD 12, and the transmission speed of the optical subscriber system is 100 Mb / s at most.
Therefore, the influence of the incidence of the received signal light on the modulation characteristics of the LD 12 can be ignored.

The 1.55 μm band signal light 6 incident on the HOE 11 from the optical fiber 19 through the optical fiber terminal and the collimating lens 21 is reflected by the interference film filter 17 shown in FIG. 2 and transmitted from the semiconductor laser 12. The signal light is combined with the signal light, further incident on the optical fiber 18, and sent to the transmission path. 1.55 transmitted from this reverse direction
The received signal light in the μm band travels backward through the above path.

Here, the loss of the hologram diffraction grating 15 that splits the 1.3 μm band transmitted / received light is determined by the ratio of the light that is transmitted without being diffracted when transmitting to the optical fiber 18. In the case of reception, it is diffracted in the θ _H direction +1.
It is determined by the proportion of second-order diffracted light. Therefore, it is important for the hologram diffraction grating type optical splitter used in this embodiment to reduce unnecessary higher order diffracted light as described in detail with reference to FIG.

Further, the hologram diffraction grating 15 is
Since the diffraction angle θ _H has wavelength dependency as shown in the equation (1), when the wavelength of the received signal light changes, the + 1st order diffracted light coupled to the PD 13 also changes. However, since the light receiving surface 62 of the PD 13 has a diameter of about 100 μm, the wavelength dependence of this diffracted light does not matter. Similarly, LD12 and PD13
The mounting error of the center distance d can also be absorbed by this light receiving diameter.

Although the LD 12 is arranged on the side of the transmitted light 2 of the hologram diffraction grating 15 in the embodiment, the LD 1
2 is combined with the + 1st order diffracted light 3 of the diffraction grating 15,
The same effect can be obtained by arranging the light beam with the transmitted light 2.

As described above, the optical module of the present invention is
The WDM coupler, splitter, and coupling optics for bidirectional transmission have been significantly downsized, and the conventional L
An optical module for transmission and reception can be realized with a size equivalent to that of a single D module.

The hologram optical element 11 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.

[0048]

As described above, according to the present invention, a wavelength division multiplexer / demultiplexer for wavelength-division multiplexing two signal lights is configured by a hologram optical element having a diffraction grating, a lens and an interference filter. Since a semiconductor laser, a photodiode, and a signal light input / output optical fiber are integrally configured, compared to the conventional optical module with a combination of individual components, the size is significantly reduced, the cost is reduced, and the mass productivity is excellent. There is an effect that it is possible to realize an optical module for transmission and reception, which is used for bidirectional transmission of the same wavelength and has a wavelength multiplexing function.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention.

FIG. 2 is a perspective view of a hologram optical element 11 used in an example.

FIG. 3 is a diagram for explaining the operation of the hologram diffraction grating 15.

FIG. 4 is a diagram showing a manufacturing procedure of the lens 16.

FIG. 5 is a perspective view showing an example of a mounting structure of a semiconductor laser 12 and a photodiode 13 used in this embodiment.

FIG. 6 is a configuration diagram of a conventional transmitting / receiving optical module.

[Explanation of Codes] 1 incident light 2 transmitted light 3 diffracted light 4 transmitted signal light 5 received signal light 6 signal light 11 hologram optical element 11a substrate 12 semiconductor laser 13 photodiode 14 support 15 hologram diffraction grating 16 lens 17 interference film filter 18, 19 Optical fiber 20, 21 Collimating lens 22 Optical fiber terminal 23 Optical fiber terminal 24 Package 25 Semiconductor package 41 Lens substrate 42 Metal mask 43 Alkaline solution 44 Ion exchange part 45 Plano-convex lens 61 Chip end surface 62 Light receiving surface 63, 64 Bonding pad 65,66 Bonding wire 67 Transmitted light 68 Received light 71 Semiconductor laser module 72 Photodiode module 73 3dB splitter 74 WDM coupler

Claims (3)

[Claims] 1. The first light of the first wavelength received on the surface of the substrate from the straight traveling direction is branched into a first transmitted straight traveling light that transmits in the straight traveling direction and a first transmitted diffracted light that diffracts in the first direction. Then, the second light of the second wavelength received from the first direction on the front surface of the substrate is reflected in the straight traveling direction, and the third light of the first wavelength received from the straight traveling direction is received on the back surface of the substrate in the straight traveling direction. A hologram optical element that transmits the fourth light of the first wavelength received from the first direction on the back surface of the substrate in the straight direction;
A semiconductor laser for supplying either the third or fourth light to the back surface of the substrate of the hologram optical element, and the third or fourth light generated in the straight traveling direction of the front surface of the substrate of the hologram optical element. Transmission signal light coupling means for optically coupling either one to the first optical fiber;
Optical signal from a second optical fiber to the hologram optical element. 2. The diffraction grating, wherein the hologram optical element is formed on the back surface of the substrate and diffracts the light of the first wavelength,
An interference film filter which is formed on the surface of the substrate and transmits the light of the first wavelength and reflects the light of the second wavelength, and the light of the first wavelength formed between the diffraction grating and the interference film filter. The optical module according to claim 1, further comprising a lens for condensing light. 3. The optical module further comprises a photodiode that receives either the first transmitted straight light or the transmitted diffracted light generated on the back surface of the substrate of the hologram optical element. Optical module.