JP5240537B2 - Optical module - Google Patents

Description

  The present invention relates to an improvement of an optical module used for one-way or two-way optical communication. In optical communication, an optical signal is generated from one node by a semiconductor laser (LD), the optical signal is transmitted through an optical fiber, and read out by a photodiode (PD) at the other node. Some use two optical fibers for transmission and reception, and others use one optical fiber for transmission and reception. A semiconductor laser (LD), a light emitting diode (LED), or the like is used as the light source. Here, what uses LD as a light source is a problem.

  When it is desired to send as many signals as possible using a single optical fiber, wavelength division multiplexing is used. Two or more signal lights Λ1, Λ2,... With different wavelengths are generated by different LDs at different nodes, propagated through one optical fiber, separated by wavelength at the exit side, and taken out by different PDs at different nodes. Try to detect.

  A WDM (Wavelength Multiplexer) or the like is used as a multiplexer that synthesizes light of different wavelengths and a demultiplexer that separates light of different wavelengths. When a signal flows in one direction, there are a plurality of transmission nodes at one end of the optical fiber. Let it be U1, U2, U3... Um. At the other end there are the same number of receiving nodes. Let it be W1, W2, W3,..., Wm. The light sources of all transmission nodes are semiconductor lasers LD1, LD2, LD3,..., LDm having different oscillation wavelengths. The oscillation wavelengths are different such as Λ1, Λ2, Λ3,. Since light of different wavelengths Λ1, Λ2, Λ3,..., Λm can be completely separated by the duplexer, there should be no fear of interference between different nodes.

  FIG. 19 shows a simplified optical communication system. This is m = 2 for simplicity, but the same thing happens with general m. LD1 of U1 generates transmission light of ΛA. This passes through the optical fiber 38, the multiplexer 39, the optical fiber 40, the duplexer 42, and the optical fiber 43 and enters the PD1 of the receiving node W1. However, although it is a little from U2, the light of ΛA may enter PD1 of W1 and become noise.

  Similarly, the receiving side W2 receives the signal light of ΛB of U2, but the light of ΛB of U1 is slightly mixed. That becomes noise. Therefore, the signal light from U2 and the noise of U1 enter W2. This is a case where there are only two pairs. However, if there are m pairs and they transmit and receive signal light through the unified optical fiber 40, one signal light (m− The noise light of 1) may enter.

  If the central office and the terminal ONU are each connected by a single optical fiber and bidirectional communication is performed to send an analog signal and a digital signal, there is still a possibility of interference. FIG. 20 shows an outline of such a wavelength division multiplexing optical communication apparatus. There are a node Ua that transmits and receives digital signals and a node Ub that transmits analog signals on the central office side. Ua includes an LDa that changes a digital signal into an optical signal of ΛA and a PDa that receives the digital signal Λc. The Ua digital signal is transmitted as a ΛA optical signal, and reaches the PDc of the terminal Wc through the optical fiber 48, the multiplexer (WDM) 49, and the optical fiber 50, and is received thereby. The LDe of the terminal ONU generates a digital signal of wavelength Λc and transmits it to the PDa of the central office Ua through the optical fiber 50, the multiplexer (WDM) 49, and the optical fiber 48.

  With this alone, 1: 1 bi-directional communication is performed, but in addition, an analog signal ΛB is transmitted from the LDb at the wavelength ΛB from the central office Ub. The analog signal passes through the optical fiber 54, the multiplexer (WDM) 49, and the optical fiber 50 and enters the PD of Wc. In such a case, the two lasers LDa and LDb in the central station cause interference in PDc and PDd, although the oscillation wavelengths ΛA and ΛB are different. Although the multiplexer (WDM) 49 is functioning normally, interference occurs. It's strange.

  Where is the cause? The present inventor has made various studies on the cause. As a result, the cause of interference was identified. The semiconductor laser is said to generate stimulated emission light having a single wavelength Λ. However, in fact, other faint light is also generated. According to the theory of laser oscillation, when inversion distribution occurs due to current, when stimulated emission occurs, all excited electrons return to the ground state simultaneously and oscillate with the same phase and the same wavelength. It is described that when the excitation energy exceeds the threshold value, all the energy is absorbed in the mode of the common phase and wavelength, and only light of one wavelength Λ is emitted.

  But that is not the case. When electrons return to the ground state, they emit light with energy corresponding to the difference between the levels of the conduction band and the valence band. However, electrons in the conduction band also have kinetic energy, and also move to holes in the valence band. There is energy. So even if the electron-hole pair disappears from the conduction band to the valence band, the energy is slightly different. There is room for multiple longitudinal modes due to different energies. Even if there is only one longitudinal mode, light other than Λ is weak.

  In the case of a gas laser where the gain is small and the resonator length is long and reciprocates many times and is finally amplified to a predetermined energy, light other than Λ is weak. However, when the resonator length is short and the gain is large as in a semiconductor laser, light other than the oscillation wavelength Λ still exists. Although the presence of such light has never been noticed before, the present inventor has realized that light of wavelengths other than Λ is emitted from the semiconductor laser. This is referred to here as spontaneous emission light.

  The meaning is a little different from the spontaneous emission that appears in laser theory. Originally, lasers start from a solid-state laser or a gas laser, and the excitation level is clear, and the energy difference between the inversion levels is uniquely determined. It does not mean that there are various energy levels. Therefore, the wavelength of the generated light is determined as one. Spontaneous emission light is also the same wavelength as oscillation light. Spontaneously emitted light comes in phase and becomes oscillating light. If the phase was the same, it was oscillation light, and if the phase was random, it was spontaneous emission light. In any case, the wavelength (energy) of the oscillation light and the spontaneous emission light was the same.

  However, in the case of a semiconductor laser, light is emitted not by transition between two levels but by current injection, so the wavelength of light emitted by electron-hole pairs is also different. Here, spontaneous emission is used as a broader term in ordinary laser engineering. The meaning is different from the spontaneous emission light used in ordinary laser optics based on the explanation of gas lasers. Here, the light emission with different energy and wavelength is not called the spontaneous emission light Σn but the phase is not different. It should not be confused with the usual meaning of spontaneous emission. To emphasize the meaning of including many wavelengths, Σ is used as a symbol.

  FIG. 21 is a wavelength spectrum of a semiconductor laser emitting light at Λq (for example, 1490 nm). The horizontal axis is wavelength and the vertical axis is power (dB). The laser oscillation light is taken as a reference of 0 dB. A peak of high power output appears at the desired wavelength. But not only that, there is a continuous spectrum of weak power on either side of the peak. This has been overlooked in the past. Not only the phase is different, but also the wavelength (energy) is different. Here, it is called spontaneous emission light Σn. On the other hand, light of a predetermined wavelength emitted from the laser is called laser oscillation light Λq. The spontaneous emission light Σn is weak such as −40 dB to −50 dB. However, even if it is weak, spontaneous emission light exists.

  It is thought that such spontaneously emitted light may have caused interference in FIGS. In FIG. 19, both the signal light ΛB of the LD2 on the transmission side and the noise light ΛB of LD1 enter the PD2 on the reception side and are sensed. PD2 receives both signal light of wavelength ΛB and spontaneous emission light. Naturally emitted light is noise. In FIG. 19, PD1 receives both spontaneous emission light from LD2 and oscillation light from LD1. Any PD receives noise having the same wavelength as the signal light. Even if the multiplexer (WDM) 39 and the demultiplexer 42 are functioning normally, the wavelengths match, so such noise cannot be blocked by WDM. The present invention makes such interference caused by spontaneous emission light a problem.

  Since it has not been known so far that a semiconductor laser emits spontaneous emission light having different wavelengths, the problem of interference that occurs when two or more semiconductor laser lights having different oscillation wavelengths pass through the same optical fiber is noticed. There is no literature. We have not been able to find prior literature that raised such a problem and showed a way to solve it.

Japanese Patent Application Laid-Open No. 2003-229626 “Optical Module, Optical Transmitter, and WDM Optical Transmitting Device”

  In Patent Document 1, since the oscillation wavelength of the semiconductor laser deviates from a predetermined value, the back light of the semiconductor laser is checked with a photodiode for wavelength monitoring, and the semiconductor laser control circuit returns the wavelength when the wavelength deviates. is there. The idea of Patent Document 1 is that the heat sink is extended backward so that back light does not leak. This makes the fluctuation of the oscillation light itself of the semiconductor laser a problem and prevents the fluctuation of the oscillation light wavelength. It does not say that there is spontaneous emission light other than the oscillation wavelength Λ. It seems that he believes that all the energy is collected in the light of the oscillation wavelength. Japanese Patent Laid-Open No. 2004-151867 does not consider the interference caused by spontaneous emission light.

  As mentioned earlier, spontaneous emission light, such as a solid-state laser, has the same wavelength as the oscillation light and is out of phase, and it is recognized that light with a different wavelength is emitted in the case of a semiconductor laser. There is no. In other words, the present invention is not aware of spontaneous emission light, which is a continuous spectrum with different wavelengths. So there is no recognition that it will prevent interference. In this field, it can be said that the spontaneous emission of the semiconductor laser itself is a novel discovery. Therefore, there is no conventional technology that prevents interference. Such a prior art could not be found.

  Semiconductor laser light includes not only oscillation light whose wavelength phase is uniquely determined, but also spontaneous emission light having a different wavelength and a different phase. Interference occurs between semiconductor lasers that should emit different wavelengths due to the presence of spontaneous emission when wavelength multiplexing optical communication is performed. It is interference that cannot be eliminated even if WDM is devised. The present invention relates to a wavelength division multiplexing optical communication system in which optical signals of different wavelengths are propagated to one optical fiber using semiconductor lasers having different oscillation lights in parallel, and an optical communication system that eliminates interference between different semiconductor lasers and light receiving elements. The purpose is to give.

  The optical module of the present invention is provided with a filter between the semiconductor laser and the optical fiber that passes only the oscillation light out of the light emitted from the semiconductor laser and blocks light of the other wavelengths. The light (spontaneously emitted light) is prevented from entering the optical fiber. Since it is complicated to say “a filter that passes oscillation light and blocks other light”, it is simply referred to as “spontaneous emission light blocking filter”.

  That is, the basic of the optical module of the present invention is a semiconductor laser that emits laser oscillation light Λq and spontaneous emission light Σn, an optical fiber that guides the light of the semiconductor laser, a lens that focuses the light of the semiconductor laser onto the optical fiber, It includes a spontaneous emission light blocking filter NF that is provided between the semiconductor laser and the optical fiber and transmits the laser oscillation light Λq of the semiconductor laser and blocks the spontaneous emission light Σn. Since the purpose is to attenuate crosstalk, there are a plurality of such basic units, and they introduce signal light into the same optical fiber. More generally expressed as follows.

  The general form of the optical module of the present invention consisting of a set of m basic forms is as follows: m semiconductor lasers LDj (j = 1, 2,..., m) emitting laser oscillation light Λqj and spontaneous emission light Σnj; M branch optical fibers Fj (j = 1, 2,..., M) for guiding the light of the laser LDj, one optical fiber F0 for collectively transmitting the signal lights of the m branch optical fibers Fj, and a semiconductor A lens Lj (j = 1, 2,..., M) that condenses the light of the laser LDj on the optical fiber Fj and the laser oscillation light Λqj provided between the semiconductor laser LDj and the optical fiber Fj are transmitted. A spontaneous emission blocking filter NFj (j = 1, 2,..., M) that blocks spontaneous emission Σnj in the vicinity of the wavelength of Λqi (i ≠ j) other than Λqj. In other words, formally, it becomes as follows.

LD1 + L1 + NF1 + F1
LD2 + L2 + NF2 + F2
......
LDj + Lj + NFj + Fj
......
LDm + Lm + NFm + Fm + F0

And so on. F1 + F2 +... + Fm → F0, and the signals are collected in one optical fiber by the multiplexing element. On the receiving side, it is separated for each wavelength by a branch element (WDM). F0 → F1 + F2 + F3... Fm, which are distributed to the optical system of m different light receiving elements.

F0 + F1 + L1 + PD1
F2 + L2 + PD2
...
Fj + Lj + PDj
...
Fm + Lm + PDm

  Since it includes a plurality of transmission LDs, there is a possibility of crosstalk. Here, a device for one of the optical systems (LDj + Lj + NFj + Fj) will be described. The same applies to other optical systems.

  A spontaneous emission blocking filter is inserted between the semiconductor laser and the optical fiber, but the light from the semiconductor laser is squeezed by the lens and incident on the end face of the optical fiber, so the spontaneous emission blocking filter and the lens are arranged in series. It will be. Any of them may be arranged closer to the semiconductor laser. In some cases, an isolator is used so that there is no return light. In that case, three elements (lens, isolator, spontaneous emission blocking filter) are arranged between the semiconductor laser and the end face of the optical fiber. Although there are six possible cases for the three contexts, any of them may be used. The spontaneous emission blocking filter can be made of a thin dielectric multilayer film, but it can also be attached to the semiconductor laser end face or deposited. On the other hand, a spontaneous emission blocking filter can be attached to the end face of the optical fiber and evaporated. Alternatively, a spontaneous emission light blocking filter can be attached to the lens surface and the isolator surface and evaporated.

  As shown in FIG. 22, the most ideal spontaneous emission blocking filter has a transmittance spectrum with a window having a transmittance of 100% only for the signal light wavelength Λq, and the transmittance is 0% for other Σn. That's it. The width ΔΛ of the transmission window is 10 nm to 100 nm and is determined depending on the purpose. The spontaneous emission blocking filter can be made by stacking a large number of two types of dielectric thin films having different refractive indexes. However, a filter having a sharp step characteristic as shown in FIG. 22 increases the number of layers and the manufacturing cost.

  If the multi-wavelength optical system uses only two wavelengths ΛA and ΛB, the design of the spontaneous emission blocking filter can be further simplified. The spontaneous emission blocking filter provided immediately after the semiconductor laser LDb that emits ΛB has a high transmittance in a finite wavelength range including ΛB as shown in FIG. 24, and the transmittance should be close to 0 in ΛA. In the meantime, it may be a filter having a convex transmittance distribution that gently reduces the transmittance. This is not to block all the spontaneous emission light of the semiconductor laser LDa but to block the spontaneous emission light in the vicinity of the wavelength of the counterpart. Since PDa does not receive light of other wavelengths, it is sufficient to remove only ΛB of LDb.

  If only two wavelengths ΛA and ΛB are used, a filter with a transmittance distribution as shown in FIG. 25 may be simplified. This is such that the transmittance at ΛB is close to 100%, the transmittance at ΛA is close to 0%, and the transmittance gradually changes from 100% to 0% in the middle. Although there is a considerable transmittance at wavelengths above ΛA, there is no problem even if the spontaneous emission light leaks around it. If ΛA does not enter PDc, it is good.

  When the magnitude relationship between the wavelengths ΛA and ΛB is opposite, a filter having a transmittance distribution as shown in FIG. 26 may be provided immediately after the semiconductor laser LDa.

  Even if it is called a spontaneous emission blocking filter, it is only necessary to remove the spontaneous emission light of the wavelength of the other party. Therefore, a filter having a gentle transmittance distribution as shown in FIGS. With such a filter, a filter having a desired performance can be manufactured using a dielectric multilayer film having a small number of layers.

  In the optical module of the present invention, signal light is introduced into an optical fiber after spontaneous emission light contained in the emitted light of the semiconductor laser is removed by a spontaneous emission light blocking filter. In an optical system in which signals of a plurality of semiconductor lasers having different wavelengths are passed through one optical fiber, the present invention can suppress crosstalk between different signal systems.

  For example, signal lights of wavelengths ΛA and ΛB from two semiconductor lasers LD1 and LD2 as shown in FIG. 19 are combined by a multiplexer (WDM) 39 and transmitted through the same optical fiber 40, and separated by a duplexer 42. In an optical system in which signal light of ΛA and ΛB are received by the two light receiving elements PD1 and PD2, respectively, a spontaneous emission light blocking filter 8 for cutting spontaneous emission light other than ΛA is provided immediately after LD1. FIG. 27 shows an optical system to which such an improvement according to the present invention is added. Spontaneous emission light blocking filters 8 and 8 for cutting spontaneous emission light other than ΛA and ΛB are provided immediately after LD1 and LD2. Then, the ΛB noise from LD1 disappears. PD2 on the receiving side receives only the signal light of ΛB of LD2. ΛB noise from LD1 does not enter and crosstalk disappears.

  Alternatively, the signal lights of the wavelengths ΛA and ΛB from the two semiconductor lasers LDa and LDb as shown in FIG. 20 are combined by the multiplexer (WDM) 49 and transmitted through the same optical fiber 50, and the splitter on the subscriber side Wc In an optical system in which the two light receiving elements PDc and PDd receive the signal light of ΛA and ΛB, respectively, a spontaneous emission blocking filter 8 for cutting the spontaneous emission light of ΛA is provided immediately after LDa. A spontaneous emission blocking filter 8 that cuts spontaneous emission other than ΛB is provided immediately after LDb. FIG. 28 shows the improved type. ΛB noise from LDa disappears. The PDd on the receiving side receives only the signal light of ΛB of LDb. ΛB noise from LDa does not enter and crosstalk disappears.

  Not only when the signal lights of two semiconductor lasers having different wavelengths are transmitted through one optical fiber, but also the signal lights ΛA, ΛB, ΛC,... Of semiconductor lasers LDa, LDb, LDc. In the wavelength division multiplexing system in which the light is passed through the same optical fiber and separated on the opposite side by a demultiplexer (WDM) and received by PDa, PDc, PDd. By providing a filter, crosstalk can be effectively prevented.

Next, a design example of the spontaneous emission blocking filter when Λq = 1490 nm is shown.
This is designed to reflect all spontaneously emitted light of wavelengths other than Λq. So there are many layers. Using BK7 glass as a substrate, an antireflection film is formed on one surface, and a spontaneous emission blocking filter is formed on the other surface.

The transparent dielectric material uses a combination of SiO ₂ and Nb ₂ O ₅ . In addition, SiON, AlN, TiO ₂ , Al ₂ O ₃ , Si, or the like can be used.

An antireflection film comprising on one surface of the BK7 glass substrate from _{Nb 2 O} 5 / SiO 2, and the other one surface to form a spontaneous emission light blocking filter by laminating 40 pairs of layers of _{Nb 2 O} 5 / SiO 2.

This is an example of a spontaneous emission light blocking filter exhibiting ideal characteristics. It is an excellent spontaneous emission blocking filter having step characteristics as shown in FIG. Therefore, although the number of layers is large, the number of layers can be further reduced if the filter is as shown in FIGS.

  Next, an embodiment in which the position of the spontaneous emission blocking filter is variously changed in a system including a semiconductor laser, a lens, an optical fiber, or an isolator will be described.

[Example 1 (FIG. 1; LD + lens + filter + optical fiber)]
Example 1 is shown in FIG. A lens 6 and an optical fiber 7 are provided on the output side optical axis of the semiconductor laser (LD) 5. Between the lens 6 and the optical fiber 7, a spontaneous emission blocking filter 8 that cuts the spontaneous emission of the semiconductor laser (LD) 5 is provided. The light from the semiconductor laser (LD) 5 is focused by the lens 6 and forms an image on the end face of the optical fiber. The semiconductor laser (LD) 5 generates spontaneous emission light Σn having different wavelengths together with oscillation light having a desired wavelength Λq. However, since the spontaneous emission blocking filter 8 blocks the spontaneous emission light Σn, the remainder is only the laser oscillation light Λq. Only the oscillation light enters the optical fiber 7. When a spontaneous emission blocking filter is provided between the lens and the optical fiber, light rays are incident at a shallow angle with respect to the optical axis, and the filter characteristics are stabilized.

[Example 2 (FIG. 2; LD + filter + lens + optical fiber)]
Example 2 is shown in FIG. A lens 6 and an optical fiber 7 are provided on the output side optical axis of the semiconductor laser (LD) 5. Between the semiconductor laser (LD) 5 and the lens 6, a spontaneous emission light blocking filter 8 that cuts the spontaneous emission light of the semiconductor laser 5 is provided. The semiconductor laser (LD) 5 generates spontaneous emission light Σn having different wavelengths together with oscillation light having a desired wavelength Λq. However, since the spontaneous emission blocking filter 8 blocks the spontaneous emission light Σn, the remainder is only the laser oscillation light Λq. Only the oscillation light enters the optical fiber 7. If a spontaneous emission blocking filter is provided between the LD and the lens, the airtight sealing can be performed integrally, and the module can be miniaturized.

[Example 3 (FIG. 3; LD + lens + filter + optical fiber)]
Example 3 is shown in FIG. On the emission side optical axis of the semiconductor laser (LD) 5, a lens 6, a spontaneous emission blocking filter 8, and an optical fiber 7 are provided in this order. The filter 8 is inclined in order to eliminate the reflected return light from the filter 8 to the semiconductor laser. The spontaneous emission light Σn included in the light of the semiconductor laser (LD) 5 is blocked by the spontaneous emission light blocking filter 8, so that only the laser oscillation light Λq is incident on the optical fiber 7.

[Example 4 (FIG. 4; LD + filter + lens + optical fiber)]
Example 4 is shown in FIG. On the emission-side optical axis of the semiconductor laser (LD) 5, a spontaneous emission blocking filter 8, a lens 6 and an optical fiber 7 are provided in this order. The filter 8 is inclined in order to eliminate the reflected return light from the filter 8 to the semiconductor laser. The spontaneous emission light Σn included in the light of the semiconductor laser (LD) 5 is blocked by the spontaneous emission light blocking filter 8, so that only the laser oscillation light Λq is incident on the optical fiber 7.

[Example 5 (FIG. 5; LD + lens with filter + optical fiber)]
FIG. 5 shows a fifth embodiment. A lens 6 and an optical fiber 7 are provided in this order on the emission side optical axis of the semiconductor laser (LD) 5. This is the same as the previous examples, but the spontaneous emission blocking filter 8 is attached to the emission surface of the semiconductor laser (LD) 5. Since the filter 8 is a dielectric multilayer film, the area is arbitrary. Here, a small area filter is bonded to the exit surface of the LD 5. By doing so, a jig for attaching the spontaneous emission blocking filter 8 to the holder or the like can be omitted. The action is the same as before. The spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn contained in the light of the LD 5, and only the laser oscillation light Λq is incident on the optical fiber 7.

[Example 6 (FIG. 6; LD + lens + filtered optical fiber)]
A sixth embodiment is shown in FIG. A semiconductor laser (LD) 5, a lens 6, and an optical fiber 7 are provided in a straight line in this order. A spontaneous emission blocking filter 8 is attached to the incident surface of the optical fiber 7. Since the filter only needs to be between the optical fiber 7 and the LD 5, the same effect can be obtained even if the filter is attached to the optical fiber 7. When the spontaneous emission blocking filter 8 is directly attached to the optical fiber, a jig to be attached to the holder or the like can be omitted. The action is the same, the spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn contained in the light of the LD 5, and only the laser oscillation light Λq is incident on the optical fiber 7. The filter is tilted and there is no reflected return light to the semiconductor laser.

[Example 7 (FIG. 7; LD + lens with filter + optical fiber)]
FIG. 7 shows a seventh embodiment. A semiconductor laser (LD) 5, a lens 6, and an optical fiber 7 are provided in a straight line in this order. A spontaneous emission blocking filter 8 is attached to the exit surface side of the lens 6. By doing so, the filter becomes a curved surface instead of a flat surface, but the effect of removing spontaneously emitted light and allowing only laser oscillation light to pass through remains unchanged. Since the filter only needs to be between the optical fiber 7 and the LD 5, the same effect can be obtained even if it is attached to the lens 6. When the spontaneous emission blocking filter 8 is directly attached to the lens 6, a jig attached to a holder or the like can be omitted. The action is the same, the spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn contained in the light of the LD 5, and only the laser oscillation light Λq is incident on the optical fiber 7.

[Example 8 (FIG. 8; LD + lens with filter + optical fiber)]
FIG. 8 shows an eighth embodiment. A semiconductor laser (LD) 5, a lens 6, and an optical fiber 7 are provided in a straight line in this order. A spontaneous emission blocking filter 8 is attached to the incident surface side of the lens 6. The action is the same, the spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn contained in the light of the LD 5, and only the laser oscillation light Λq is incident on the optical fiber 7. When the spontaneous emission blocking filter 8 is directly attached to the lens 6, a jig attached to a holder or the like can be omitted.

[Example 9 (FIG. 9; LD + lens + filter + isolator + optical fiber)]
FIG. 9 shows a ninth embodiment. The present invention can also be applied to an optical system in which an isolator is added to what has been described so far. The application to an optical system including an isolator will be described below. A semiconductor laser (LD) 5, a lens 6, a spontaneous emission blocking filter 8, and an optical fiber 7 are provided in a straight line in this order. An isolator 9 is attached to the incident surface of the optical fiber 7. The isolator 9 is provided in order to prevent the light from the LD 5 from entering the optical fiber and reflecting off the other end of the optical fiber and returning to the LD. A spontaneous emission blocking filter 8 is provided between the lens 6 and the optical fiber 7 and blocks the spontaneous emission Σn contained in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7. Since the light beam is incident at a shallow angle with respect to the optical axis while suppressing the reflected return light to the LD, the spontaneous emission light can be stably filtered.

[Example 10 (FIG. 10; LD + lens + filter, optical fiber with isolator)]
A tenth embodiment is shown in FIG. This also has an isolator. A semiconductor laser (LD) 5, a lens 6, and an optical fiber 7 are provided in a straight line in this order. A spontaneous emission blocking filter 8 and an isolator 9 are attached to the incident surface of the optical fiber 7. As in the previous example, the isolator 9 is for preventing reflected return light. A spontaneous emission light blocking filter 8 is provided in front of the optical fiber 7 and blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7. In this configuration, a mounting jig such as a filter holder can be omitted.

[Example 11 (FIG. 11; LD + lens + isolator, optical fiber with filter)]
Example 11 is shown in FIG. This also has an isolator. A semiconductor laser (LD) 5, a lens 6, and an optical fiber 7 are provided in a straight line in this order. An isolator 9 and a spontaneous emission blocking filter 8 are attached to the incident surface of the optical fiber 7. As in the previous example, the isolator 9 is for preventing reflected return light. A spontaneous emission light blocking filter 8 is provided in front of the optical fiber 7 and blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7. In this configuration, a mounting jig such as a filter holder can be omitted.

[Example 12 (FIG. 12; LD + lens + filter + isolator + optical fiber)]
FIG. 12 shows a twelfth embodiment. On the extension of the optical axis of the semiconductor laser (LD) 5, a lens 6, a filter 8, an isolator 9, and an optical fiber 7 are provided in this order. A spontaneous emission blocking filter 8 is provided between the lens 6 and the isolator 9. The spontaneous emission blocking filter 8 is located in front of the isolator 9 and the optical fiber 7 and blocks the spontaneous emission Σn contained in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7.

[Example 13 (FIG. 13; LD + lens + isolator with filter + optical fiber)]
FIG. 13 shows a thirteenth embodiment. On the extension of the optical axis of the semiconductor laser (LD) 5, a lens 6, an isolator 9 with a filter 8, and an optical fiber 7 are provided in this order. A spontaneous emission blocking filter 8 is attached to the front surface of the isolator 9. The spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7. In this configuration, a mounting jig such as a filter holder can be omitted.

Example 14 (FIG. 14; LD + lens + isolator with filter + optical fiber)
FIG. 14 shows a fourteenth embodiment. On the extension of the optical axis of the semiconductor laser (LD) 5, a lens 6, an isolator 9 with a filter 8, and an optical fiber 7 are provided in this order. A spontaneous emission blocking filter 8 is attached to the rear surface of the isolator 9. The spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7. In this configuration, a mounting jig such as a filter holder can be omitted.

[Example 15 (FIG. 15; LD + lens + isolator + filter + wavelength selection filter + lens + PD + optical fiber)]
FIG. 15 shows a fifteenth embodiment. Examples 15 to 18 are examples in which the present invention is applied to a transmission / reception module (LD / PD) that transmits signals bidirectionally in a single optical fiber. On the extension of the optical axis of the semiconductor laser (LD) 5, a lens 6, an isolator 9, a spontaneous emission light blocking filter 8, a 45-degree inclined wavelength selection filter 4, and an optical fiber 7 are provided in this order. A PD 25 and a lens 26 are provided in a direction symmetrical to the LD 5 and the lens 6 with respect to the wavelength selection filter 4. A noise wavelength cutoff filter 28 is provided between the lens 26 and the wavelength selection filter 4. The received light that has passed through the optical fiber 7 is reflected by the wavelength selection filter 4, bends the optical path by 90 degrees, passes through the noise wavelength cutoff filter 28, is narrowed by the lens 26, and enters the PD 25. With this configuration, light rays are incident at a shallow angle with respect to the optical axis, and the filter characteristics are stabilized. Therefore, a single-core transmission / reception module that stably filters spontaneously emitted light can be realized.

  The 45-degree inclined wavelength selection filter 4 has a function of transmitting the transmission light of the LD 5 and reflecting the reception light. It can be made of a dielectric multilayer film. The noise wavelength cutoff filter 28 on the PD side is a filter that passes only the wavelength of the received light. This is originally present in the wavelength division multiplexing transmission / reception module and extracts only the reception wavelength of the node. Even so, the starting point of the present invention is that since spontaneously emitted light of that wavelength from another node enters, it cannot prevent interference. In the case of wavelength multiplexing, the spontaneous emission blocking filter 8 blocks the spontaneous emission Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7.

The isolator can be omitted. In this configuration, the spontaneous emission blocking filter 8 is provided between the isolator 9 and the 45-degree inclined wavelength selection filter 4, but may be provided between the isolator 9 and the lens 6. Further, the spontaneous emission blocking filter 8 may be formed on the surface of the 45-degree inclined wavelength selection filter 4 on the side close to the semiconductor laser (LD) 5.

[Example 16 (FIG. 16; LD + filter + lens + isolator + wavelength selection filter + lens + PD + optical fiber)]
Example 16 is shown in FIG. This is also an example applied to a transmission / reception module (LD / PD) that sends signals bidirectionally in a single optical fiber. On the extension of the optical axis of the semiconductor laser (LD) 5, a spontaneous emission blocking filter 8, a lens 6, an isolator 9, a 45-degree inclined wavelength selection filter 4, and an optical fiber 7 are provided in this order. A noise wavelength cutoff filter 28, a PD 25, and a lens 26 are provided in a direction symmetrical to the LD 5 and the lens 6 with respect to the wavelength selection filter 4. The received light that has passed through the optical fiber 7 is reflected by the wavelength selection filter 4, bends the optical path by 90 degrees, passes through the noise wavelength cutoff filter 28, is narrowed by the lens 26, and enters the PD 25. The noise wavelength cutoff filter 28 on the PD side is a filter that passes only the wavelength of the received light. The spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7. In this configuration, the LD, the spontaneous emission blocking filter and the lens can be hermetically sealed together, and the module can be downsized. The isolator can be omitted. Note that the spontaneous emission blocking filter 8 may be formed on the surface of the lens 6.

[Example 17 (FIG. 17; LD + lens + isolator + wavelength selection filter + lens + PD + spontaneous emission blocking filter + optical fiber)]
FIG. 17 shows Example 17. This is also an example applied to a transmission / reception module (LD / PD) that sends signals bidirectionally in a single optical fiber. On the extension of the optical axis of the semiconductor laser (LD) 5, a lens 6, an isolator 9, a 45-degree inclined wavelength selection filter 4, a spontaneous emission blocking filter 8, and an optical fiber 7 are provided in this order. A noise wavelength cutoff filter 28, a PD 25, and a lens 26 are provided in a direction symmetrical to the LD 5 and the lens 6 with respect to the wavelength selection filter 4. In this example, the spontaneous emission blocking filter 8 can transmit the semiconductor laser oscillation light Λq and the received light. The received light that has passed through the optical fiber 7 is reflected by the wavelength selection filter 4, bends the optical path by 90 degrees, passes through the noise wavelength cutoff filter 28, is narrowed by the lens 26, and enters the PD 25. The spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7.
The isolator can be omitted. With this configuration, light rays are incident at a shallow angle with respect to the optical axis, and the filter characteristics are stabilized. Therefore, a single-core transmission / reception module that stably filters spontaneously emitted light can be realized.

[Embodiments 18 and 19 (FIGS. 18 and 29; LD + spontaneous emission blocking filter + lens + wavelength selection filter + wavelength selection filter + PD + lens + filter + PD + lens + filter + optical fiber)]
FIG. 18 shows Example 18. This is a 3-port module that uses two PDs and one LD. On the extension of the optical axis of the semiconductor laser (LD) 5, a spontaneous emission blocking filter 8, a lens 6, a 45 ° tilt wavelength selection filter 64, a 45 ° tilt wavelength selection filter 4, and an optical fiber 7 are provided in this order. It is done. A PD 25, a lens 26, and a filter 28 are provided in a direction symmetrical to the LD 5 and the lens 6 with respect to the wavelength selection filter 4. A PD 65, a lens 66, and a filter 68 are provided in a direction symmetrical to the LD 5 and the lens 6 with respect to the wavelength selection filter 64. Received light of a certain wavelength that has propagated through the optical fiber 7 is reflected by the wavelength selection filter 4, passes through the filter 28, is collected by the lens 26, and enters the PD 25. Received light of another wavelength that has propagated through the optical fiber 7 is reflected by the wavelength selection filter 64, passes through the noise wavelength cutoff filter 68, is collected by the lens 66, and enters the PD 65. The spontaneous emission light is removed from the light from the LD 5 by the spontaneous emission blocking filter 8. Further, the light is squeezed by the lens 6 and passes through the 45 ° tilt wavelength selection filter 64 and the opposite 45 ° tilt wavelength selection filter 4 and enters the optical fiber 7. The spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7.

 In this configuration, the LD, the spontaneous emission blocking filter, and the lens can be sealed in one piece, and the module can be downsized.

  The spontaneous emission blocking filter 8 may be provided between the lens 6 and the wavelength selection filter 64 (FIG. 29; Example 19). In this configuration, light rays are incident at a shallow angle with respect to the optical axis, and the filter characteristics are stabilized.

[Example 20 (FIG. 30; LD + lens + spontaneous emission light blocking filter + isolator + wavelength selection filter + wavelength selection filter + PD + lens + filter + PD + lens + filter + optical fiber)]
FIG. 30 shows a twentieth embodiment. This is also a 3-port type module using two PDs and one LD. On the extension of the axis of the semiconductor laser (LD) 5, the lens 6, the isolator 9 with the spontaneous emission blocking filter 8 attached thereto, the 45 ° tilt wavelength selection filter 64, the 45 ° tilt wavelength selection filter 4 in the opposite direction, the light Fiber 7 is provided in order. A PD 25, a lens 26, and a noise wavelength cutoff filter 28 are provided in a direction symmetrical to the LD 5 and the lens 6 with respect to the wavelength selection filter 4. A PD 65, a lens 66, and a filter 68 are provided in a direction symmetrical to the LD 5 and the lens 6 with respect to the wavelength selection filter 64. Received light of a certain wavelength that has propagated through the optical fiber 7 is reflected by the wavelength selection filter 4, passes through the noise wavelength cutoff filter 28, is collected by the lens 26, and enters the PD 25. Received light of another wavelength that has propagated through the optical fiber 7 is reflected by the wavelength selection filter 64, passes through the filter 68, is collected by the lens 66, and enters the PD 65. The light from the LD 5 is focused by the lens 6 and the spontaneous emission light is removed by the spontaneous emission blocking filter 8. The light enters the optical fiber 7 through the isolator 9, the 45 ° tilt wavelength selection filter 64, and the 45 ° tilt wavelength selection filter 4 in the opposite direction. The spontaneous emission light blocking filter 8 blocks the spontaneous emission light Σn included in the light of the LD 5. Only the laser oscillation light Λq is incident on the optical fiber 7.

Since the spontaneous emission blocking filter 8 is affixed to the isolator 9, a mounting jig such as a filter holder can be omitted.
Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

1 is an optical system configuration diagram of an optical module according to a first embodiment in which optical components are arranged in series in the order of a semiconductor laser, a lens, a spontaneous emission blocking filter, and an optical fiber.

The optical system block diagram which concerns on Example 2 which has arrange | positioned the optical components in series in order of the semiconductor laser, the spontaneous emission blocking filter, the lens, and the optical fiber.

The optical system block diagram of the optical module which concerns on Example 3 which has arrange | positioned the optical components in series in order of the semiconductor laser, the lens, the inclination spontaneous emission light cutoff filter, and the optical fiber.

The optical system block diagram which concerns on Example 4 which has arrange | positioned the optical components in series in order of the semiconductor laser, the inclination spontaneous emission light cutoff filter, the lens, and the optical fiber.

The optical system block diagram of the optical module which concerns on Example 5 which has arrange | positioned the optical components in order of the semiconductor laser which formed the spontaneous emission light cutoff filter in the output surface, the lens, and the optical fiber in order.

The optical system block diagram which concerns on the optical module which concerns on Example 6 which has arrange | positioned the optical components in order of the optical fiber which formed the semiconductor laser, the lens, and the spontaneous emission light cutoff filter in the incident end surface.

The optical system block diagram which concerns on the optical module which concerns on Example 7 which has arrange | positioned the optical components in order of the semiconductor laser, the lens which formed the spontaneous emission light cutoff filter in the output surface, and the optical fiber.

The optical system block diagram of the optical module which concerns on Example 8 which has arrange | positioned the optical component in order of the semiconductor laser, the lens which formed the spontaneous emission light cutoff filter in the incident surface, and the optical fiber in order.

The optical system block diagram of the optical module which concerns on Example 9 which has arrange | positioned the optical components in order of the semiconductor fiber, the lens, the spontaneous emission light cutoff filter, and the optical fiber which affixed the isolator on the end surface.

The optical system block diagram of the optical module which concerns on Example 10 which has arrange | positioned the optical components in order of the optical fiber which affixed the semiconductor laser, the lens, the isolator, and the spontaneous emission light cutoff filter on the end surface.

The optical system block diagram of the optical module which concerns on Example 11 which has arrange | positioned the optical component in order of the semiconductor fiber, the lens, the spontaneous emission light cutoff filter, and the optical fiber which affixed the isolator on the end surface in order.

The optical system block diagram of the optical module which concerns on Example 12 which has arrange | positioned the optical components in series in order of the semiconductor laser, the lens, the spontaneous emission light cutoff filter, the isolator, and the optical fiber.

The optical system block diagram of the optical module which concerns on Example 13 which has arrange | positioned the optical component in order of the semiconductor laser, the lens, the isolator which affixed the spontaneous emission light cutoff filter on the incident side, and the optical fiber in order.

The optical system block diagram of the optical module which concerns on Example 14 which has arrange | positioned the optical component in order of the semiconductor laser, the lens, the isolator which stuck the spontaneous emission light cutoff filter on the output side, and the optical fiber.

A semiconductor laser, lens, isolator, spontaneous emission blocking filter, wavelength selection filter, and optical fiber are arranged in series, and a noise wavelength blocking filter, lens, and photodiode are provided on the reflection side of the wavelength selection filter to transmit and receive light on the optical fiber. The optical system block diagram of the optical module which concerns on Example 15 made to propagate light to a photodiode.

A semiconductor laser, a spontaneous emission blocking filter, a lens, an isolator, a wavelength selection filter, and an optical fiber are arranged in series. A noise wavelength blocking filter, a lens, and a photodiode are provided on the reflection side of the wavelength selection filter. The optical system block diagram of the optical module which concerns on Example 16 made to propagate received light to a photodiode.

A semiconductor laser, a lens, an isolator, a wavelength selection filter, a spontaneous emission blocking filter, and an optical fiber are arranged in series. A noise wavelength blocking filter, a lens, and a photodiode are provided on the reflection side of the wavelength selection filter. The optical system block diagram of the optical module which concerns on Example 17 made to propagate a received light to a photodiode.

Semiconductor laser, spontaneous emission blocking filter, lens, 45 degree tilt wavelength selection filter, 45 degree tilt wavelength selection filter in opposite direction, optical fiber arranged in series, two sets of noise wavelengths on the reflection side of the two wavelength selection filters FIG. 18 is an optical system configuration diagram of an optical module according to Example 18 in which a cutoff filter, a lens, and a photodiode are provided, and transmission light and two types of reception light are propagated to an optical fiber.

In a wavelength division multiplexing optical communication system in which a transmission side having two semiconductor lasers LD1 and LD2 and a reception side having two light receiving elements PD1 and PD2 are connected by a single optical fiber, ΛB noise of LD1 and ΛB signal of LD2 The optical system block diagram explaining that crosstalk occurs because light enters PD2 on the receiving side.

In an optical communication system in which a node having the semiconductor lasers LDa and PDa and a node having the semiconductor laser LDb are connected with two light receiving elements PDc and PDd and the node having the semiconductor laser LDe by one optical fiber, the LDA ΛB The optical system block diagram explaining that crosstalk occurs because noise and signal light of ΛB of LDb enter PDd on the receiving side.

Semiconductor laser oscillation spectrum. In addition to the oscillation light of Λq, weak light having different wavelengths is emitted. Noise light and level is not constant. Here, it is called spontaneous emission light Σn.

FIG. 4 is a transmittance wavelength characteristic diagram of a spontaneous emission blocking filter having a step-type transmittance change in which only oscillation light is strictly transmitted and spontaneous emission light on both sides is reflected.

FIG. 6 is a spectrum diagram of transmitted light when a spontaneous emission blocking filter that causes a step-type change between oscillation light and spontaneous emission light is placed in front of a semiconductor laser.

One laser has 100% transmittance at the oscillation wavelength ΛB, and the other laser has a transmittance of 0% at wavelengths longer than ΛA and ΛB, but the spontaneous emission is blocked with a moderate change in transmittance. The transmittance distribution diagram of the filter.

Transmittance distribution of a spontaneous emission light blocking filter that has 100% transmittance at the oscillation wavelength ΛB of one laser and 0% transmittance at the other oscillation wavelength ΛA, but the transmittance gradually changes in the middle. Figure.

Transmittance distribution of a spontaneous emission blocking filter that has 100% transmittance at the oscillation wavelength ΛA of one laser and 0% transmittance at the other oscillation wavelength ΛB of the other laser, but the transmittance gradually changes in the middle. Figure.

The optical system block diagram which shows an example of this invention which erase | eliminated the crosstalk in the optical system of FIG. 19 by providing the spontaneous emission light cutoff filter in front of the semiconductor laser.

The optical system block diagram which shows an example of this invention which erase | eliminated the crosstalk by providing the spontaneous emission light cutoff filter in front of the semiconductor laser in the optical system of FIG.

Semiconductor laser, lens, spontaneous emission blocking filter, 45 degree tilt wavelength selection filter, 45 degree tilt wavelength selection filter in opposite directions, optical fiber arranged in series, two sets of filters on the reflection side of the two wavelength selection filters, FIG. 20 is an optical system configuration diagram of an optical module according to Example 19 in which a lens and a photodiode are provided, and transmission light and two types of reception light are propagated to an optical fiber.

A semiconductor laser, a lens, an isolator with a spontaneous emission blocking filter, a 45-degree tilt wavelength selection filter, a 45-degree tilt wavelength selection filter in the opposite direction, and an optical fiber are arranged in series, and two sets are provided on the reflection side of the two wavelength selection filters. The optical system block diagram of the optical module which concerns on Example 20 which provided the filter, the lens, and the photodiode, and was made to propagate two types of receiving light to a photodiode in an optical fiber.

Explanation of symbols

4 wavelength selection filter 5LD
6 lenses
7 optical fibers
8 Spontaneous emission blocking filter
9 isolator
25PD
26 lenses
28 noise wavelength cut filter 29 lens 38 optical fiber
39 multiplexer
40 optical fiber
42 duplexer
43 optical fiber
44 optical fiber
45 optical fiber
48 optical fiber
49 multiplexer
50 optical fiber
54 optical fiber
64-wavelength selection filter 65PD
66 lenses
68 noise cutoff filter
Λq laser oscillation light
Σn spontaneous emission
ΛA LDa, LD1 oscillation light wavelength ΛB LDb, LD2 oscillation light wavelength LDa, LDb, LDe Semiconductor laser
PDa, PDc, PDd, PD1, PD2 Photodiode

Claims (16)

A semiconductor laser having a short cavity length and emitting laser oscillation light Λq and spontaneous emission light Σn having a wavelength different from that of the laser oscillation light to the outside of the cavity, an optical fiber for guiding the light of the semiconductor laser, and a semiconductor A lens that condenses the laser light on the optical fiber, and a natural light that is provided between the semiconductor laser and the optical fiber and transmits the laser oscillation light Λq emitted from the semiconductor laser resonator to the outside of the semiconductor laser and blocks the spontaneous emission light Σn. An optical module comprising an emission light blocking filter. A semiconductor laser having a short resonator length and emitting laser oscillation light Λq and spontaneous emission light Σn having a wavelength different from that of the laser oscillation light to the outside of the resonator can be connected to an optical fiber for guiding the light of the semiconductor laser. Laser oscillation light emitted from the semiconductor laser resonator to the outside of the semiconductor laser provided between the connector, a lens for condensing the light of the semiconductor laser to a connector capable of connecting the optical fiber, and a connector capable of connecting the semiconductor laser and the optical fiber An optical module comprising a spontaneous emission blocking filter that transmits Λq and blocks spontaneous emission Σn.   The optical module according to claim 1, wherein a spontaneous emission blocking filter is provided between the lens and the optical fiber. The optical module according to claim 2, wherein a spontaneous emission blocking filter is provided between the lens and the connector.   The optical module according to claim 1, wherein a spontaneous emission blocking filter is provided between the semiconductor laser and the lens.   6. The light according to claim 3, wherein the spontaneous emission blocking filter is provided to be inclined rather than perpendicular to the optical axis connecting the semiconductor laser (LD) and the optical fiber. module.   6. The optical module according to claim 4, wherein the spontaneous emission blocking filter is provided to be inclined rather than perpendicular to the optical axis connecting the semiconductor laser (LD) and the connector. .   3. The optical module according to claim 1, wherein a spontaneous emission blocking filter is attached to the lens surface of the lens. A semiconductor laser having a short resonator length, emitting a transmitted light and emitting it to the outside of the resonator, a connector capable of connecting an optical fiber for guiding the light of the semiconductor laser, and the light of the semiconductor laser A transmission lens that focuses light on an optical fiber, a photodiode that receives received light, a reception lens that focuses received light on a photodiode, and a light that is placed on the optical path of the transmitted light is separated by wavelength. In an optical module comprising a wavelength selection filter and a noise wavelength cut-off filter placed on an optical path of received light for separating light according to wavelength, the light is emitted to the outside of the semiconductor laser resonator between the semiconductor laser and the connector. An optical module comprising a spontaneous emission blocking filter that transmits the emitted laser oscillation light and blocks spontaneous emission light having a wavelength different from that of the laser oscillation light . A semiconductor laser having a short cavity length, which emits transmission light and emits it to the outside of the cavity, an optical fiber for guiding the light of the semiconductor laser, and the light of the semiconductor laser in the optical fiber. A transmitting lens that emits light, a photodiode that receives the received light, a receiving lens that collects the received light on the photodiode, and a wavelength selection filter that is placed on the optical path of the transmitted light and separates the light according to the wavelength. In an optical module comprising a noise wavelength blocking filter for separating light according to wavelength, placed on the optical path of the received light, a laser beam emitted to the outside of the semiconductor laser resonator between the semiconductor laser and the optical fiber. An optical module comprising a spontaneous emission blocking filter that transmits the oscillation light and blocks spontaneous emission light having a wavelength different from that of the laser oscillation light .   11. The optical module according to claim 9, further comprising at least one of the receiving lens, the photodiode, the wavelength selection filter, and a noise wavelength cutoff filter.   The optical module according to claim 9 or 10, wherein the spontaneous emission blocking filter is provided between the transmission lens and a wavelength selection filter placed on an optical path of the transmission light.   The optical module according to claim 9, wherein the spontaneous emission blocking filter is inclined rather than perpendicular to an optical axis connecting the semiconductor laser, the wavelength selection filter, and the connector.   The optical module according to claim 10, wherein the spontaneous emission blocking filter is inclined rather than perpendicular to an optical axis connecting the semiconductor laser, the wavelength selection filter, and the optical fiber.   11. The optical module according to claim 9, wherein a spontaneous emission blocking filter is formed on a surface of the wavelength selective filter close to the semiconductor laser. The optical module according to claim 9 or 10, wherein a spontaneous emission blocking filter is formed on a lens surface of the transmitting lens.

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