JPH01292917A - Photodetecting module - Google Patents

Abstract

PURPOSE:To prevent the self-oscillation of a semiconductor optical amplifying element by respectively defining an input coupling space and an output coupling space as optical long-range coupling due to parallel rays and arranging the respective types of optical devices in these coupling spaces. CONSTITUTION:An inputted optical signal and an amplifying signal, which is outgoing from a semiconductor optical amplifying element 106, are caused to be the parallel rays respectively in the input coupling space and output coupling space. Thus, the optical coupling between an input fiber 102 and the semiconductor optical amplifying element 106 and between the output coupling space, namely, the semiconductor optical amplifying element 106 and a photo- detecting element 111 can be defined as the long-range coupling and the various optical devices, etc., can be arranged in these coupling spaces. Here, isolators 104 and 108, which are arranged in the respective input coupling space and output coupling space, transmit only a light to be emitted from an optical fiber 101 to the photo-detecting element 111. Thus, the self-oscillation of the semiconductor optical amplifying element 106 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a semiconductor light receiving module which is a photoelectric converter used in optical communications and optical transmission lines.

(Prior Art) Optical semiconductor elements such as photodiodes are used as light receiving elements that convert optical signals into electrical signals.

Here, by placing a semiconductor optical amplification element in front of the light receiving element and amplifying the optical signal once before inputting it to the light receiving element,
Efforts are being made to increase transmission distance and improve transmission quality.

Conventionally, devices of this type are, for example, ELECTRONIC
8LETTER8vol, 23. A20 (198
There was something that was disclosed in September 2007). That is, as shown in FIG. 2, an optical fiber 1 having a tapered end and a hemispherical lens tip is optically coupled to a semiconductor optical amplifying element 2. As shown in FIG. This amplification element 2 amplifies the optical signal input from the optical fiber 1 and outputs it as an amplified signal. This amplified signal is focused by a focusing lens 3 and is incident on a light receiving element 4. With such a configuration, a stronger electrical signal can be obtained as an output than when the amplification element 2 is not used.

(Problems to be Solved by the Invention) However, in addition to amplifying input light, the semiconductor optical amplifying element also emits spontaneous emission light. For example, spontaneous emission light emitted from the input side of the amplification element is reflected by the end face of the optical fiber 1, enters the amplification element 2, is amplified, and is emitted from the output side. A portion of this emitted light is reflected by the incident surface of the lens 3 or the light receiving element 4, enters the amplification element 2 again, is amplified, and is emitted from the input side surface. As described above, there is a problem in that the amplification element 2 causes laser oscillation due to reflection of the spontaneously emitted light by the optical fiber 1, the lens 3, and the light receiving element.

In addition, this spontaneous emission light contains many wavelengths other than the input optical signal, so when this spontaneous emission light enters the light receiving element, the electric signal outputted by optical-to-electrical conversion includes the above-mentioned natural emission light. This will include a lot of beat noise caused by the emitted light. For this reason, there was a problem that the S/N ratio of the output electric signal decreased.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light-receiving module that can eliminate the above-mentioned problems, prevent self-oscillation of a semiconductor optical amplification element, and suppress a decrease in the S/N ratio of an output electric signal.

(Means for Solving the Problems) In order to solve the above problems, the present invention optically couples an input optical signal to a semiconductor optical amplification element via an input coupling space, and amplifies the amplified signal by the amplification element. In a light-receiving module that optically couples a signal to a light-receiving element via an output coupling space and converts the amplified signal into an electrical signal by the light-receiving element, means for converting the optical signal and the amplified signal into parallel beams, respectively. A first isolator is provided in the input coupling space, and a second isolator is provided in the output coupling space, and a filter for removing spontaneously emitted light from the amplification element.

(Function) The optical signal input to the light receiving module and the amplified signal output from the semiconductor optical amplification element are respectively input to the input coupling space and
Parallel rays are formed in the output coupling space. Therefore, the optical coupling between the input coupling space, that is, between the input fiber and the semiconductor optical amplifier element, and the output coupling space, that is, between the semiconductor optical amplifier element and the light receiving element, can be made into a long-distance coupling. Various optical devices and the like can be arranged within the coupling space of.

The isolators arranged in each of the input coupling space and the output coupling space transmit only light directed from the optical fiber to the light receiving element. Therefore, self-oscillation of the semiconductor optical amplification element can be prevented.

Further, the filter disposed in the output coupling space removes the spontaneous emission light of the semiconductor optical amplification element from the amplified signal.

(Example) FIG. 1 is a block diagram showing an example of the present invention. 10
0 is a gnocage that accommodates each component of the light-receiving monomer. An optical signal propagated through an optical transmission line (not shown) is input to the light receiving module through an input fiber 101. This optical signal is transmitted to the input fiber package inner end surface 10.
2 into the package 100. first lens 1
03 is a lens that converts the emitted optical signal into parallel light beams. The parallel optical signal passes through the first isolator 104, is focused by the second lens 105, and is sent to a semiconductor optical amplification element (hereinafter referred to as "amplification element") 106.
incident on . This amplification element 106 amplifies the incident optical signal and outputs it as an amplified signal.

The third lens 107 converts the emitted amplified signal into parallel light beams. The amplified signal, which has become a parallel beam, is
The light passes through the second isolator 10g and enters the filter 109. This filter 109 is for removing the spontaneously emitted light from the amplification element 106 as well as the amplified signal. The amplified signal that has passed through this filter 109 enters the fourth lens 110 and then enters the light receiving element 111. This light-receiving element 111 converts the input amplified signal into a current, and outputs it from the light-receiving module in the form of an electric signal.

For the first to fourth lenses, ball lenses, Cellfora lenses, or the like are used. By converting the optical signal and the amplified signal into parallel light beams through these lenses, the optical signals between the input fiber end face 102 and the amplification element 106 and between the amplification element 106 and the light receiving element 111 are The coupling can be an optical long-range coupling. It is desirable that the surfaces of the first to fourth lenses be coated with anti-reflection coating to reduce reflection when the optical signal or amplified signal enters and exits.

The first and second isolators are arranged to prevent the amplification element 106 from laser oscillating. That is, these isolators allow light to pass only in the forward direction, with the direction from the input fiber 102 to the light receiving element 111 being the forward direction, and the opposite direction being the reverse direction. By arranging these isolators, for example, spontaneous emission light emitted from the incident surface of the amplification element 106 is blocked by the isolator 104 and does not reach the input fiber end face 102, and therefore is reflected by the input fiber end face 102 and is emitted from the amplification element 106. It does not enter the element 106 again. On the other hand, the spontaneously emitted light emitted from the output surface of the amplifying element 106 passes through a filter 109 and a fourth lens 110, and then passes through the light receiving element 1.
Reach 11.

However, even if this spontaneously emitted light is reflected by these filters 109, the fourth lens 110, or the light receiving element 111, this reflected light is blocked by the second isolator 108 and does not enter the amplifying element 106 again. There isn't.

Note that the spontaneous emission light from the amplification element 106 is
Since the reflected light is also reflected by the third lens, these reflected lights enter the amplification element 106 again. but,
The amount of these reflected lights is very small and does not affect the function of the amplification element 1060. If anti-reflection coating is applied to the second and third lenses, the amount of reflected light will be further reduced.

The filter 109 has the wavelength of the input signal as its center wavelength, removes spontaneous emission light included in the amplified signal, and prevents wavelengths other than the wavelength of the input signal from entering the light receiving element 111.

(Effects of the Invention) As described above in detail, according to the present invention, the input coupling space between the input fiber and the semiconductor optical amplification element and the output coupling space between the semiconductor optical amplification element and the light receiving element are respectively By using long-distance optical coupling using parallel light beams and arranging the first isolator in the input coupling space and the second isolator and filter in the output coupling space, self-oscillation of the semiconductor optical amplification element can be prevented. Furthermore, it is possible to reduce the beat noise generated by optical-to-electrical conversion of the spontaneously emitted light of the semiconductor optical amplification element, and to improve the S/N ratio of the output electrical signal.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the light receiving module of the present invention, and the second
The figure is a diagram showing the configuration of a conventional light receiving module. 101... Optical fiber, 102... Input fiber end face, 103... First lens, 104... First isolator, 105... Second lens, 106...
Semiconductor optical amplification element, 107...Third lens, 10B
...Second isolator, 109...Filter, 1
10... Fourth lens, 111... Light receiving element. Patent Applicant Oki Electric Industry Co., Ltd. Product v, - KQ Procedural Amendment (Mutsu) l Indication of the case 1988 Patent Teruon No. 1218052 Name of the invention Photoreceptor Mosoul3 Relationship with the person making the amendment Application for patent Personnel office (
Address: 105) 1-7-12 Toranomon, Minato-ku, Tokyo Telephone: (454) 2111 Inugo ・ 6 Contents of the amendment t's- 4 Ko 0 Shi 1

Claims (1)

[Claims] An input optical signal is optically coupled to a semiconductor optical amplification element via an input coupling space, and an amplified signal amplified by this amplification element is optically coupled to a light receiving element via an output coupling space. The light-receiving module converts the amplified signal into an electrical signal by the light-receiving element, further comprising means for converting the optical signal and the amplified signal into parallel beams, and a first isolator is provided in the input coupling space. . A light receiving module, wherein the output coupling space includes: a second isolator; and a filter for removing spontaneously emitted light from the amplification element.