JP2014199995A - Optical receiver - Google Patents

Optical receiver Download PDF

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JP2014199995A
JP2014199995A JP2013074418A JP2013074418A JP2014199995A JP 2014199995 A JP2014199995 A JP 2014199995A JP 2013074418 A JP2013074418 A JP 2013074418A JP 2013074418 A JP2013074418 A JP 2013074418A JP 2014199995 A JP2014199995 A JP 2014199995A
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signal
polarization
light
local oscillation
separated
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佑治 速水
Yuji Hayami
佑治 速水
利夫 片岡
Toshio Kataoka
利夫 片岡
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Sumitomo Osaka Cement Co Ltd
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Abstract

PROBLEM TO BE SOLVED: To provide an optical receiver with a simplified structure and small dependence on wavelength.SOLUTION: An optical receiver demodulates a multi-value phase modulation signal corresponding to each polarization using signal light S in which each independent multi-value phase modulation signal is added to two types of orthogonal polarization, and local oscillation light R with the same wavelength as the signal light (linear polarization). The optical receiver comprises: composite wave signal generation means that separates the signal light into two separate signal lights S1, S2 corresponding to each polarization, converts the two separate signal lights into circular polarization, separates the local oscillation light into two separate local oscillation lights R1, R2, combines the circular-polarization converted separation signal lights and the separation local oscillation lights such that their polarization planes will form a prescribed angle, and forms and outputs two composite wave signals L1-L4 per separate signal light; and IQ output means that is made up of polarization and separation elements for separating and outputting an I signal and a Q signal corresponding to each polarization from the composite wave signals L1-L4. The polarization direction of the local oscillation light has a prescribed angle with the polarization axis of the polarization and separation elements.

Description

本発明は、光受信器に関し、特に、直交する2偏波に各々独立した多値位相変調信号を復調する光受信器に関する。   The present invention relates to an optical receiver, and more particularly to an optical receiver that demodulates a multilevel phase modulation signal that is independent of two orthogonally polarized waves.

光通信技術の一つに、DP−QPSK(Dual Polarization
Quadrature Phase Shift Keying)、BPSK(Binary Phase Shift
Keying)、QAM(Quadrature Amplitude Modulation)等に代表される直交する2偏波に各々独立した多値位相変調信号を印加する通信方式が提案されている。このような信号光を復調するには、偏波間において90度位相差をもった光を偏光ビームスプリター(Polarizing Beam Splitter。PBS)にて偏波分離し、I信号(In-phase信号)とQ信号(Quadrature-phase信号)の光出力を得ることが行われている。
DP-QPSK (Dual Polarization) is one of the optical communication technologies.
Quadrature Phase Shift Keying), BPSK (Binary Phase Shift)
There has been proposed a communication method in which independent multilevel phase modulation signals are applied to two orthogonally polarized waves represented by Keying) and QAM (Quadrature Amplitude Modulation). In order to demodulate such signal light, light having a phase difference of 90 degrees between polarized waves is polarized and separated by a polarizing beam splitter (PBS), and an I signal (In-phase signal) and a Q signal are separated. An optical output of a signal (Quadrature-phase signal) is obtained.

本出願人は、特許文献1において、小型化が可能な光90度ハイブリッドを用いた光受信器を提案した。光90度ハイブリッドの構成を図1に示す。図1の光受信器の動作を説明すると、垂直偏波の局部発振光は、λ/4波長板に入力され円偏光に偏波変換され、その次のハーフミラーで分岐される。一方、信号光は、任意の偏波状態で偏光ビームスプリッタ(PBS)に入力され、垂直偏波と水平偏波に分離される。PBSによって得られた垂直偏波と水平偏波とは、各々λ/2波長板に入力され、斜め45度直線偏波に変換される。斜め45度直線偏波に変換された信号光は、それぞれ円偏波の局部発振光と合波され、その後PBSに入力されることで、位相差90度を有するI信号及びQ信号を得ている。   In the patent document 1, the present applicant proposed an optical receiver using an optical 90-degree hybrid that can be reduced in size. The structure of the light 90-degree hybrid is shown in FIG. The operation of the optical receiver shown in FIG. 1 will be described. Vertically polarized local oscillation light is input to a λ / 4 wavelength plate, converted into circularly polarized light, and branched by the next half mirror. On the other hand, the signal light is input to a polarization beam splitter (PBS) in an arbitrary polarization state, and is separated into vertical polarization and horizontal polarization. The vertically polarized wave and the horizontally polarized wave obtained by the PBS are respectively input to the λ / 2 wavelength plate and converted into an oblique 45-degree linearly polarized wave. The signal light converted into 45-degree obliquely linearly polarized light is combined with the circularly polarized local oscillation light and then input to the PBS to obtain an I signal and a Q signal having a phase difference of 90 degrees. Yes.

図1の光受信器では、局部発振光の入力側と信号光の入力側に、それぞれ異なる波長板を必要とし、このため、光受信器の構成が複雑化していた。また、波長板は波長依存性を有するため、多くの種類の波長板を使用することは光変調器の波長依存性を強め、光学特性の劣化に繋がっていた。   The optical receiver of FIG. 1 requires different wavelength plates on the local oscillation light input side and the signal light input side, respectively, which complicates the configuration of the optical receiver. Further, since the wave plate has wavelength dependency, the use of many types of wave plates strengthens the wavelength dependency of the optical modulator and leads to deterioration of optical characteristics.

特開2012−182790号公報JP 2012-182790 A

本発明が解決しようとする課題は、上述したような問題を解決し、構造をより単純化でき、波長依存性の少ない光受信器を提供することである。   The problem to be solved by the present invention is to provide an optical receiver that solves the above-described problems, can simplify the structure, and has less wavelength dependency.

上記課題を解決するため、本発明は以下のような技術的特徴を有する。
(1) 直交する2偏波に各々独立した多値位相変調信号が付与された信号光(S)と、信号光と同一波長(直線偏波)である局部発振光(R)とを用いて、各偏波に応じた該多値位相変調信号を復調する光受信器において、該信号光(S)を各偏波に対応して2つの分離信号光(S1,S2)に分離し、前記2つの分離信号光(S1,S2)を円偏光に変換し、該局部発振光(R)を2つの分離局部発振光(R1,R2)に分離し、前記分離信号光(S1)と該分離局部発振光(R1)とを合波して合波光を生成し、前記分離信号光(S2)と該分離局部発振光(R2)とを合波して合波光を生成し、前記各合波光毎に2つの合成波信号(L1〜L4)を形成して出力する、空間光学系で構成される合成波信号生成手段と、該合成波信号(L1〜L4)から各偏波に対応するI信号及びQ信号を分離して出力する、偏波分離素子からなる空間光学系で構成されるIQ出力手段とを備え、該局部発振光(R)の偏光方向は、該偏波分離素子の偏光軸と所定の角度を有することを特徴とする。
In order to solve the above problems, the present invention has the following technical features.
(1) Using signal light (S) in which independent multi-level phase modulation signals are assigned to two orthogonal polarizations, and local oscillation light (R) having the same wavelength (linear polarization) as the signal light In the optical receiver that demodulates the multi-level phase modulation signal corresponding to each polarization, the signal light (S) is separated into two separated signal lights (S1, S2) corresponding to each polarization, Two separated signal lights (S1, S2) are converted into circularly polarized light, the local oscillation light (R) is separated into two separated local oscillation lights (R1, R2), and the separated signal light (S1) and the separation are separated. The combined oscillation light is combined with the local oscillation light (R1) to generate combined light, and the separated signal light (S2) and the separated local oscillation light (R2) are combined to generate combined light. A synthesized wave signal generating unit configured by a spatial optical system that forms and outputs two synthesized wave signals (L1 to L4) every time, and the synthesized wave signal (L 1 to L4) and an IQ output means composed of a spatial optical system composed of polarization separation elements for separating and outputting the I signal and Q signal corresponding to each polarization, and the local oscillation light (R) The polarization direction has a predetermined angle with the polarization axis of the polarization separation element.

(2) 上記(1)に記載の光受信器において、該局部発振光(R)の偏光方向と該偏波分離素子の偏光軸とがなす所定の角度は45度であることを特徴とする。 (2) In the optical receiver described in (1) above, the predetermined angle formed by the polarization direction of the local oscillation light (R) and the polarization axis of the polarization separation element is 45 degrees. .

(3) 上記(1)又は(2)に記載の光受信器において、該IQ出力手段は、偏光ビームスプリッタを用いてI信号及びQ信号に分離するよう構成されていることを特徴とする。 (3) In the optical receiver described in the above (1) or (2), the IQ output means is configured to separate an I signal and a Q signal using a polarization beam splitter.

(4) 上記(1)乃至(3)のいずれかに記載の光受信器において、該合成波信号生成手段を構成する光学部品と該IQ出力手段を構成する光学部品とは、線膨張係数が略等しいことを特徴とする。 (4) In the optical receiver according to any one of the above (1) to (3), the optical component constituting the combined wave signal generating means and the optical component constituting the IQ output means have a linear expansion coefficient. It is characterized by being substantially equal.

本発明のように、直交する2偏波に各々独立した多値位相変調信号が付与された信号光(S)と、信号光と同一波長(直線偏波)である局部発振光(R)とを用いて、各偏波に応じた該多値位相変調信号を復調する光受信器において、該信号光(S)を各偏波に対応して2つの分離信号光(S1,S2)に分離し、前記2つの分離信号光(S1,S2)を円偏光に変換し、該局部発振光(R)を2つの分離局部発振光(R1,R2)に分離し、前記分離信号光(S1)と該分離局部発振光(R1)とを合波して合波光を生成し、前記分離信号光(S2)と該分離局部発振光(R2)とを合波して合波光を生成し、前記各合波光毎に2つの合成波信号(L1〜L4)を形成して出力する、空間光学系で構成される合成波信号生成手段と、該合成波信号(L1〜L4)から各偏波に対応するI信号及びQ信号を分離して出力する、偏波分離素子からなる空間光学系で構成されるIQ出力手段とを備え、該局部発振光(R)の偏光方向は、該偏波分離素子の偏光軸と所定の角度を有することにより、波長板の数を削減でき、構造が単純化すると共に偏波依存性の少ない光受信器を提供することが可能となる。   As in the present invention, signal light (S) in which independent multi-level phase modulation signals are given to two orthogonal polarizations, and local oscillation light (R) having the same wavelength (linear polarization) as the signal light, In the optical receiver that demodulates the multi-level phase modulation signal corresponding to each polarization, the signal light (S) is separated into two separated signal lights (S1, S2) corresponding to each polarization Then, the two separated signal lights (S1, S2) are converted into circularly polarized light, the local oscillation light (R) is separated into two separated local oscillation lights (R1, R2), and the separated signal light (S1) And the separated local oscillation light (R1) are combined to generate combined light, and the separated signal light (S2) and the separated local oscillation light (R2) are combined to generate combined light, Synthetic wave signal generation means composed of a spatial optical system that forms and outputs two synthetic wave signals (L1 to L4) for each combined light, and the synthesis IQ output means configured by a spatial optical system composed of polarization separation elements for separating and outputting the I signal and Q signal corresponding to each polarization from the signals (L1 to L4), and the local oscillation light ( The polarization direction of R) has a predetermined angle with the polarization axis of the polarization separation element, so that the number of wave plates can be reduced, the structure is simplified, and an optical receiver with less polarization dependency is provided. It becomes possible.

特許文献1に開示された光受信器の例を示す図である。10 is a diagram illustrating an example of an optical receiver disclosed in Patent Document 1. FIG. 本発明の光受信器の概略を説明する図である。It is a figure explaining the outline of the optical receiver of this invention. 本発明の光受信器で光路長調整板を使用する例を示す図である。It is a figure which shows the example which uses an optical path length adjustment board with the optical receiver of this invention. 本発明の光受信器で光路長調整板を位置決め手段として使用する例を示す図である。It is a figure which shows the example which uses an optical path length adjustment board as a positioning means with the optical receiver of this invention. 本発明の光受信器で結合ブロックを使用する例を示す図である。It is a figure which shows the example which uses a combination block with the optical receiver of this invention. 本発明の光受信器で光路長調整板を最終段に配置した例を示す図である。It is a figure which shows the example which has arrange | positioned the optical path length adjustment board in the last stage with the optical receiver of this invention. 本発明の光受信器でIQ出力手段を複屈折材料で構成した例を示す図である。It is a figure which shows the example which comprised IQ output means with the birefringent material with the optical receiver of this invention. 本発明の光受信器で複屈折材料と光路長調整板を使用する例を示す図である。It is a figure which shows the example which uses a birefringent material and an optical path length adjusting plate with the optical receiver of this invention.

以下、本発明の光受信器について、好適例を用いて詳細に説明する。
本発明は、図2に示すように、直交する2偏波に各々独立した多値位相変調信号が付与された信号光(S)と、信号光と同一波長(直線偏波)である局部発振光(R)とを用いて、各偏波に応じた該多値位相変調信号を復調する光受信器において、該信号光(S)を各偏波に対応して2つの分離信号光(S1,S2)に分離し、前記2つの分離信号光(S1,S2)を円偏光に変換し、該局部発振光(R)を2つの分離局部発振光(R1,R2)に分離し、前記分離信号光(S1)と該分離局部発振光(R1)とを合波して合波光を生成し、前記分離信号光(S2)と該分離局部発振光(R2)とを合波して合波光を生成し、前記各合波光毎に2つの合成波信号(L1〜L4)を形成して出力する、空間光学系で構成される合成波信号生成手段と、該合成波信号(L1〜L4)から各偏波に対応するI信号及びQ信号を分離して出力する、偏波分離素子からなる空間光学系で構成されるIQ出力手段とを備え、該局部発振光(R)の偏光方向は、該偏波分離素子の偏光軸と所定の角度を有することを特徴とする。
Hereinafter, the optical receiver of the present invention will be described in detail using preferred examples.
In the present invention, as shown in FIG. 2, signal light (S) in which independent multi-level phase modulation signals are applied to two orthogonal polarizations, and local oscillation having the same wavelength (linear polarization) as the signal light In an optical receiver that demodulates the multi-level phase modulation signal corresponding to each polarization using light (R), the signal light (S) is divided into two separated signal lights (S1) corresponding to each polarization. , S2), the two separated signal lights (S1, S2) are converted into circularly polarized light, the local oscillation light (R) is separated into two separated local oscillation lights (R1, R2), and the separation The signal light (S1) and the separated local oscillation light (R1) are combined to generate combined light, and the separated signal light (S2) and the separated local oscillation light (R2) are combined to combine light. Generating a composite wave signal composed of a spatial optical system that generates and outputs two composite wave signals (L1 to L4) for each of the combined lights. And IQ output means composed of a spatial optical system composed of polarization separation elements for separating and outputting the I signal and the Q signal corresponding to each polarization from the combined wave signals (L1 to L4), The polarization direction of the local oscillation light (R) has a predetermined angle with the polarization axis of the polarization separation element.

本発明のように、局部発振光を45度直線偏光とし、信号光側の波長板をλ/2板からλ/4板にした場合、従来の光90度ハイブリッドの光学系と比較し、局部発振光側のλ/4波長板を削除することが可能となる。その結果、光学系の構成を単純化でき、また波長依存性を有する波長板を減らすことができるため、光90度ハイブリッドの波長依存性を抑制出来る。   When the local oscillation light is 45-degree linearly polarized light and the wavelength plate on the signal light side is changed from the λ / 2 plate to the λ / 4 plate as in the present invention, it is compared with the conventional optical 90-degree hybrid optical system. It becomes possible to delete the λ / 4 wavelength plate on the oscillation light side. As a result, the configuration of the optical system can be simplified, and the wavelength plate having wavelength dependency can be reduced, so that the wavelength dependency of the optical 90-degree hybrid can be suppressed.

図2では、合成波信号生成手段(A)に対して、信号光(S)と局部発振光(R)を同じ側(図面の上側)から入射し、合成波信号(L1〜L4)を反対側(図面の下側)に出射している。さらに、IQ出力手段(B)に対して、合成波信号が入射する側(図面の上側)と反対側(図面の下側)からI信号とQ信号を出力している。これらの構成により、合成波信号生成手段やIQ出力手段から出射する光が必要以上に広がらず、光受信器のサイズを小型化することが可能となる。なお、図2では、信号光等の入射方向と、合成波信号やI信号及びQ信号の出射方向とが、互いに平行となるように構成されているが、本発明においては、必ずしも平行となる必要はなく、出力光が出力された後の光学系に合わせて適宜設計することができる。   In FIG. 2, the signal light (S) and the local oscillation light (R) are incident from the same side (upper side of the drawing) to the composite wave signal generation means (A), and the composite wave signals (L1 to L4) are opposite. The light is emitted to the side (the lower side of the drawing). Further, the IQ signal is output to the IQ output means (B) from the side (upper side of the drawing) on which the composite wave signal is incident (lower side of the drawing). With these configurations, the light emitted from the combined wave signal generation unit and the IQ output unit does not spread more than necessary, and the size of the optical receiver can be reduced. In FIG. 2, the incident direction of signal light and the like and the emission direction of the synthesized wave signal, the I signal, and the Q signal are configured to be parallel to each other. However, in the present invention, they are not necessarily parallel. It is not necessary, and can be appropriately designed according to the optical system after the output light is output.

合成波信号生成手段では、まず、信号光(S)を偏光ビームスプリッター(PBS)で2つの偏波(S1,S2)に分離し、一方の偏波S2を全反射ミラーで他方の偏波S1と同じ方向に揃えている。次に、偏波(S1,S2)を円偏光とするためλ/4波長板を通過させる。λ/4波長板を通過した偏波(S1,S2)は、当該波長板の下側に配置された全反射ミラーで、図面の横方向に反射され、偏波S1は左方向に、偏波S2は右方向に導かれる。   In the combined wave signal generating means, first, the signal light (S) is separated into two polarized waves (S1, S2) by a polarization beam splitter (PBS), and one polarized wave S2 is separated by a total reflection mirror and the other polarized wave S1. Are aligned in the same direction. Next, in order to make the polarized waves (S1, S2) circularly polarized light, it is passed through a λ / 4 wavelength plate. The polarized waves (S1, S2) that have passed through the λ / 4 wavelength plate are reflected in the horizontal direction of the drawing by a total reflection mirror disposed on the lower side of the wavelength plate, and the polarized wave S1 is polarized in the left direction. S2 is guided to the right.

他方、局部発振光(R)は、信号光と同一波長(直線偏波,特に45度直線偏光)であり、最初に通過するハーフミラーで、下方向に向かう局部発振光と右方向に向かう局部発振光の2つに分離する。下方向に向かう局部発振光は、ハーフミラーにより、偏波面を調整された偏波S1と合波され、さらに、2つの合成波信号(L1,L2)を形成する。また、右方向に向かった局部発振光は、全反射ミラーで反射され下方向に向かい、ハーフミラーにより、偏波面を調整された偏波S2と合波され、さらに、2つの合成波信号(L3,L4)を形成する。   On the other hand, the local oscillation light (R) has the same wavelength as that of the signal light (linearly polarized wave, particularly 45 degree linearly polarized light), and is a half mirror that passes first. Separated into two of oscillation light. The downwardly oscillating local oscillation light is combined with the polarized wave S1 whose polarization plane is adjusted by the half mirror, and further forms two combined wave signals (L1, L2). Further, the local oscillation light directed to the right direction is reflected by the total reflection mirror and directed downward, and is combined by the half mirror with the polarized wave S2 whose polarization plane is adjusted, and further, two combined wave signals (L3) , L4).

図2の実施例では、IQ出力手段(B)は、偏光ビームスプリッタ(PBS)を用いてI信号及びQ信号に分離するよう構成されている。   In the embodiment of FIG. 2, the IQ output means (B) is configured to separate into an I signal and a Q signal using a polarization beam splitter (PBS).

図2のような空間光学系を製造するには、偏光ビームスプリッタ(PBS)、ハーフミラー(BS)、全反射ミラー、波長板、さらに必要に応じて配置される、部品間の距離を調整するスペーサ部品を、BK7を基材として構成し、各光学部品を高精度に張り合わせる必要がある。   In order to manufacture the spatial optical system as shown in FIG. 2, the distance between the components, which are arranged as necessary, includes a polarizing beam splitter (PBS), a half mirror (BS), a total reflection mirror, a wave plate, and the like. It is necessary to configure the spacer parts using BK7 as a base material and to attach the optical parts with high accuracy.

本発明の光受信器では、C−BAND(1530nm-1565nm)、L−BAND(1565nm-1625nm)、もしくは両方の帯域において波長依存性の少ない光学膜(反射膜、ハーフミラー、偏光分離ミラーなど)を利用して空間光学系を形成することができる。しかも、BK7などのガラス部材で構成された、本発明に使用される空間光学系は、偏光依存性がある導波路素子で構成する場合と比べて、波長依存性や偏光依存性に優れた性能を発揮する。   In the optical receiver of the present invention, an optical film (reflection film, half mirror, polarization separation mirror, etc.) having little wavelength dependency in C-BAND (1530 nm-1565 nm), L-BAND (1565 nm-1625 nm), or both bands. A spatial optical system can be formed using In addition, the spatial optical system used in the present invention, which is composed of a glass member such as BK7, is superior in wavelength dependency and polarization dependency compared to a case where it is composed of a polarization dependent waveguide element. Demonstrate.

図3は、合成波信号生成手段(A)とIQ出力手段(B)との間に、各合成波信号(L1〜L4)の光路長差を調整する光路長調整手段(光路長調整板)を配置した実施例である。   FIG. 3 shows an optical path length adjusting means (optical path length adjusting plate) for adjusting the optical path length difference of each synthesized wave signal (L1 to L4) between the synthesized wave signal generating means (A) and the IQ output means (B). It is the Example which has arranged.

合成波信号生成手段(A)では、ハーフミラーで信号光と局部発振光を合波すると共に、2つの合成波信号(L1とL2,L3とL4)を生成しているが、合成波信号生成手段(A)から出力する時点で、2つの合成波信号に光路長差が発生している。この光路長差を補正するため、光路長調整手段(C)が設けられている。   The combined wave signal generation means (A) combines the signal light and the local oscillation light with a half mirror and generates two combined wave signals (L1 and L2, L3 and L4). At the time of output from the means (A), an optical path length difference is generated between the two synthesized wave signals. In order to correct this optical path length difference, optical path length adjusting means (C) is provided.

光路長調整手段(C)は、図3のように、合成波信号生成手段(A)に密着して固定配置するだけでなく、離間して配置することも可能である。ただし、図3のように、密着して配置することで、各光学部品の位置決めを、精度良く行うことが可能となり、光受信器の組立調整が容易になる。   As shown in FIG. 3, the optical path length adjusting means (C) can be arranged not only in close contact with the combined wave signal generating means (A) but also in a spaced arrangement. However, as shown in FIG. 3, the optical components can be positioned with high accuracy by being placed in close contact, and assembly adjustment of the optical receiver is facilitated.

図3の実施例では、IQ出力手段(B)において、偏光ビームスプリッタ(PBS)でI信号及びQ信号に分離した後の光路長を同じにするため、平行四辺形の断面の全面反射ミラーと台形の透明な光学部品が、当該手段の後段部分に配置されている。図2に示すIQ出力手段は、図3のような光路長の調整が行われていないため、受光素子の配置位置を調整したり、別途、光路長調整手段をIQ出力手段の下流側に配置することが必要となる。   In the embodiment of FIG. 3, in the IQ output means (B), in order to make the optical path lengths after being separated into the I signal and the Q signal by the polarization beam splitter (PBS), A trapezoidal transparent optical component is arranged in the latter part of the means. The IQ output means shown in FIG. 2 is not adjusted in the optical path length as shown in FIG. 3, so the arrangement position of the light receiving element is adjusted, or the optical path length adjustment means is separately arranged on the downstream side of the IQ output means. It is necessary to do.

図4の実施例は、合成波信号生成手段(A)と光路長調整手段(C)及びIQ出力手段(C)とを互いに密着して固定配置し、光受信器を構成する空間光学系全体を一体化したものである。これにより、光受信器を小型化することが可能になるだけでなく、各光学部品の位置決めも高精度かつ容易に行うことができる。図4の構成を採用することで、15×15mm程度の空間に、偏波分離機能を含んだ光受信器を形成することが可能となる。   In the embodiment of FIG. 4, the synthesized wave signal generating means (A), the optical path length adjusting means (C), and the IQ output means (C) are fixedly arranged in close contact with each other, and the entire spatial optical system constituting the optical receiver. Are integrated. Thereby, not only can the optical receiver be reduced in size, but also the positioning of each optical component can be performed with high accuracy and ease. By adopting the configuration of FIG. 4, an optical receiver including a polarization separation function can be formed in a space of about 15 × 15 mm.

図5の実施例は、IQ出力手段(B)は、図面の左右に、2つのIQ出力のための光学系を備えているが、これらの部品を別々に位置調整することは煩雑であるため、両者の中間に結合ブロックを配置し、全体が一つのブロック体となるよう構成している。   In the embodiment of FIG. 5, the IQ output means (B) is provided with two optical systems for IQ output on the left and right sides of the drawing, but it is complicated to position these components separately. The connecting block is arranged between the two so that the whole becomes one block body.

図6の実施例は、IQ出力手段(B)の下流側に、合成波信号生成手段で発生する各合成波信号の光路長差を補完する光路長調整板を配置したものである。このように、光路長調整板は、合成波信号生成手段(A)の下流側であれば、どの場所にも設けることは可能であるが、図6のように、IQ出力手段の下流側に配置する場合には、光出力される信号の数がより多くなるため、光路長調整板の部品点数が増加し、図3のものと比較して、調整が煩雑化する。   In the embodiment of FIG. 6, an optical path length adjusting plate that complements the optical path length difference of each synthesized wave signal generated by the synthesized wave signal generating means is arranged on the downstream side of the IQ output means (B). As described above, the optical path length adjusting plate can be provided anywhere on the downstream side of the combined wave signal generating means (A). However, as shown in FIG. 6, the optical path length adjusting plate is provided on the downstream side of the IQ output means. In the case of arrangement, since the number of signals to be optically output is increased, the number of parts of the optical path length adjusting plate is increased, and the adjustment becomes complicated as compared with that in FIG.

図7に示すように、IQ出力手段は、複屈折材料で構成される単一の光学部品とすることが可能である。複屈折材料に入射した4つの合成波信号(L1〜L4)は、偏波分離され、図7に示すように、90度の位相関係をもったI信号とQ信号の出力光となる。複屈折材料の結晶軸方向は、偏波分離した光線の進行方向に合わせて、90度の位相関係で調整される。   As shown in FIG. 7, the IQ output means can be a single optical component made of a birefringent material. The four combined wave signals (L1 to L4) incident on the birefringent material are polarized and separated, and output light of an I signal and a Q signal having a phase relationship of 90 degrees as shown in FIG. The crystal axis direction of the birefringent material is adjusted with a phase relationship of 90 degrees in accordance with the traveling direction of the polarized light beam.

さらに、複屈折材料の光進行方向の長さを調整することで、I信号とQ信号の光出力間ピッチも調整することが可能となる。図7のように、IQ信号の平行光が得られ、その出力ピッチも自由に変更できることから、I信号とQ信号の光出力をまとめて受光素子などの光検出器に光結合することが可能となる。   Furthermore, by adjusting the length of the birefringent material in the light traveling direction, the pitch between the optical outputs of the I signal and the Q signal can also be adjusted. As shown in FIG. 7, parallel light of the IQ signal is obtained, and the output pitch can be freely changed, so that the optical output of the I signal and the Q signal can be combined and optically coupled to a photodetector such as a light receiving element. It becomes.

IQ出力手段から出力される各光波は、バランスド受光素子などの光検出器により、I信号及びQ信号に対応する電気信号に変換される。   Each light wave output from the IQ output means is converted into an electrical signal corresponding to the I signal and the Q signal by a photodetector such as a balanced light receiving element.

図7のように、IQ出力手段を複屈折材料による単一の光学部品で構成する場合には、図2〜6に示したように、PBSや全反射ミラーを組み合わせた光学部品を複数配置するものと比較し、部品点数を大幅に削減することができる。これにより、光受信器における製造コストの低減することができ、部品間の複雑な調整作業も省略できるため、光学特性の劣化を防ぐことができる。ただし、複屈折材料を用いる方が、図面の縦方向の長さが長くなり、図4のものと比較して、大型化することとなる。   As shown in FIG. 7, when the IQ output means is composed of a single optical component made of a birefringent material, a plurality of optical components combined with PBS and total reflection mirrors are arranged as shown in FIGS. Compared to products, the number of parts can be greatly reduced. Thereby, the manufacturing cost in the optical receiver can be reduced, and complicated adjustment work between components can be omitted, so that deterioration of optical characteristics can be prevented. However, the use of the birefringent material increases the length in the vertical direction of the drawing, which increases the size as compared with that of FIG.

IQ出力手段を単一の光学部品で構成した場合には、IQ出力手段を位置決めの基準として利用することができ、図7に示すように、複屈折材料の上に、合成波信号生成手段を構成する複数の光学部品を固定配置することで、各光学部品を精度よく配置することが可能となる。   When the IQ output means is composed of a single optical component, the IQ output means can be used as a positioning reference. As shown in FIG. 7, the synthesized wave signal generating means is provided on the birefringent material. By fixing and arranging the plurality of optical components to be configured, it becomes possible to arrange each optical component with high accuracy.

合成波信号生成手段を構成する光学部品とIQ出力手段を構成する光学部品とは、線膨張係数を略等しく構成することが好ましい。これは、使用環境の温度変化に伴い、合成波信号生成手段とIQ出力手段との間での位置ずれが発生し、光学特性が劣化するなどの不具合が生じるのを抑制することが可能となる。当然、光路長調整手段についても同様である。   It is preferable that the optical component constituting the synthetic wave signal generating means and the optical component constituting the IQ output means have substantially the same linear expansion coefficient. This makes it possible to suppress the occurrence of problems such as the occurrence of misalignment between the synthesized wave signal generating means and the IQ output means due to the temperature change of the use environment and the deterioration of optical characteristics. . Of course, the same applies to the optical path length adjusting means.

具体的には、合成波信号生成手段を構成する光学部品は、主として光学ガラスBK7で構成することができる。また、IQ出力手段を複屈折材料で構成する場合には、YVO4が利用可能である。YVO4とBK7とは、線膨張係数がほぼ等しいため、使用環境の温度変化に伴う光学特性の劣化を抑制することが可能となる。   Specifically, the optical component constituting the synthetic wave signal generating means can be mainly constituted by the optical glass BK7. Further, when the IQ output means is made of a birefringent material, YVO4 can be used. Since YVO4 and BK7 have substantially the same linear expansion coefficient, it is possible to suppress the deterioration of the optical characteristics accompanying the temperature change in the use environment.

図8に示すように、合成波信号生成手段とIQ出力手段との間に、光路長調整板などの光路長調整手段を配置し、各合成波信号の光路長(L1とL2との間の光路長差、又はL3とL4との間の光路長差)を調整し、各合成波信号間の光路長を一致させることができる。これは、図3の実施例で説明したように、ハーフミラーで各偏波と局部発振光が合波され、その後、平行光として複屈折材料に入射させるため、各合成波信号(L1〜L4)における光路長が異なるためである。このように、複屈折材料に入射する合成波信号の光路長差を調整することで、当該複屈折率材料から出射する光波を、直接、光検出器に入射させるだけで、適正なI信号やQ信号を容易に得ることができる。   As shown in FIG. 8, an optical path length adjusting means such as an optical path length adjusting plate is arranged between the synthesized wave signal generating means and the IQ output means, and the optical path length (between L1 and L2) of each synthesized wave signal. The optical path length difference between the synthesized wave signals can be matched by adjusting the optical path length difference or the optical path length difference between L3 and L4. As described in the embodiment of FIG. 3, each polarization wave and local oscillation light are combined by a half mirror and then incident on a birefringent material as parallel light. This is because the optical path lengths in () are different. In this way, by adjusting the optical path length difference of the composite wave signal incident on the birefringent material, the light wave emitted from the birefringent material can be directly incident on the photodetector, and an appropriate I signal or The Q signal can be easily obtained.

また、IQ出力手段の後段に第2の光路長調整手段を配置し、IQ出力手段から出力される(I−1,I−2)信号と(Q−1,Q−2)信号の光路長差を調整することも可能である。これにより、より適正なI信号やQ信号を得ることができる。   Further, the second optical path length adjusting means is arranged after the IQ output means, and the optical path lengths of the (I-1, I-2) signal and the (Q-1, Q-2) signal output from the IQ output means. It is also possible to adjust the difference. Thereby, more appropriate I signal and Q signal can be obtained.

以上説明したように、本発明によれば、構造をより単純化でき、波長依存性の少ない光受信器を提供することが可能となる。   As described above, according to the present invention, it is possible to provide an optical receiver with a simpler structure and less wavelength dependency.

Claims (4)

直交する2偏波に各々独立した多値位相変調信号が付与された信号光(S)と、信号光と同一波長(直線偏波)である局部発振光(R)とを用いて、各偏波に応じた該多値位相変調信号を復調する光受信器において、
該信号光(S)を各偏波に対応して2つの分離信号光(S1,S2)に分離し、前記2つの分離信号光(S1,S2)を円偏光に変換し、該局部発振光(R)を2つの分離局部発振光(R1,R2)に分離し、
前記分離信号光(S1)と該分離局部発振光(R1)とを合波して合波光を生成し、前記分離信号光(S2)と該分離局部発振光(R2)とを合波して合波光を生成し、前記各合波光毎に2つの合成波信号(L1〜L4)を形成して出力する、空間光学系で構成される合成波信号生成手段と、
該合成波信号(L1〜L4)から各偏波に対応するI信号及びQ信号を分離して出力する、偏波分離素子からなる空間光学系で構成されるIQ出力手段とを備え、
該局部発振光(R)の偏光方向は、該偏波分離素子の偏光軸と所定の角度を有することを特徴とする光受信器。
Using each of the signal light (S) to which each of the two orthogonal polarizations is provided with an independent multilevel phase modulation signal and the local oscillation light (R) having the same wavelength (linear polarization) as the signal light, each polarization is used. In an optical receiver that demodulates the multi-level phase modulation signal according to a wave,
The signal light (S) is separated into two separated signal lights (S1, S2) corresponding to each polarization, the two separated signal lights (S1, S2) are converted into circularly polarized light, and the local oscillation light (R) is separated into two separated local oscillation lights (R1, R2);
The separated signal light (S1) and the separated local oscillation light (R1) are combined to generate a combined light, and the separated signal light (S2) and the separated local oscillation light (R2) are combined. A combined wave signal generating unit configured by a spatial optical system that generates combined light, and forms and outputs two combined wave signals (L1 to L4) for each combined light;
IQ output means configured by a spatial optical system composed of polarization separation elements that separate and output the I signal and Q signal corresponding to each polarization from the combined wave signals (L1 to L4),
An optical receiver characterized in that the polarization direction of the local oscillation light (R) has a predetermined angle with the polarization axis of the polarization separation element.
請求項1に記載の光受信器において、該局部発振光(R)の偏光方向と該偏波分離素子の偏光軸とがなす所定の角度は45度であることを特徴とする光受信器。   2. The optical receiver according to claim 1, wherein a predetermined angle formed by the polarization direction of the local oscillation light (R) and the polarization axis of the polarization separation element is 45 degrees. 請求項1又は2に記載の光受信器において、該IQ出力手段は、偏光ビームスプリッタを用いてI信号及びQ信号に分離するよう構成されていることを特徴とする光受信器。   3. The optical receiver according to claim 1, wherein the IQ output means is configured to separate into an I signal and a Q signal using a polarization beam splitter. 請求項1乃至3のいずれかに記載の光受信器において、該合成波信号生成手段を構成する光学部品と該IQ出力手段を構成する光学部品とは、線膨張係数が略等しいことを特徴とする光受信器。   4. The optical receiver according to claim 1, wherein the optical component constituting the combined wave signal generating means and the optical component constituting the IQ output means have substantially the same linear expansion coefficient. Optical receiver.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017098893A (en) * 2015-11-27 2017-06-01 住友電気工業株式会社 Optical receiver
JP2017125926A (en) * 2016-01-13 2017-07-20 住友電気工業株式会社 Optical receiver

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017098893A (en) * 2015-11-27 2017-06-01 住友電気工業株式会社 Optical receiver
JP2017125926A (en) * 2016-01-13 2017-07-20 住友電気工業株式会社 Optical receiver

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